Why aren’t there more women in the upper ranks of corporate America?

Cue the broken record: Women rein in career plans to spend more time caring for family. What’s more, they are inherently less ambitious than men and don’t have the confidence that commands seats in the C-suite.

Not so fast.

Something else is happening on the way to the top. Women aren’t abandoning their careers in large numbers; motherhood, in fact, increases their appetite for winning promotions; and women overall don’t lack for ambition and confidence that they can take on big jobs. Yet when asked whether they want a top role in their companies or industries, a majority of women say they would rather not grab the brass ring.

Those are the findings of a major new study of women in the workplace conducted by LeanIn.Org and McKinsey & Co. The research, which gathered data on promotions, attrition and trajectories from 118 companies and surveyed nearly 30,000 men and women, is among the largest efforts to capture attitudes and data about working women. The study involved major North American companies and North American units of global ventures headquartered elsewhere. It reveals sharply different views of the workplace, in which women say they experience a playing field at work that is anything but level.

Roughly equal numbers of men and women say they want to be promoted—78% and 75%, respectively. But as men’s desire for big jobs intensifies in the course of their careers, only 43% of women said they want to be a top executive, compared with 53% of men. Perhaps most startling, 25% of women feel their gender has hindered their progress, a perception that grows more acute once women reach senior levels.

Overall, just over a quarter of female survey respondents say that their organization is a meritocracy. Women certainly face a steeper path to the top than men do, making up just 17% of the population of the executive suite, the end result of promotion patterns that favor men at every level. And attrition isn’t the issue, the study found—women are less likely than men to leave their companies, particularly once they reach the senior and executive levels.

In the end, according to the survey, women are 15% less likely than men to be promoted to the next level—and at the current pace, it will be more than a century before there is gender equality in the C-suite.

The message for corporations: There’s a lot of work to do, and it starts at the top.

While three-quarters of companies tracked by Lean In and McKinsey named gender diversity as a priority of the chief executive, fewer than half of employees surveyed said it was high on their own CEO’s priority list. Only a third of men and women say that advancing women is a priority for their direct boss—a phenomenon that Stanford University professor Shelley Correll calls the “frozen middle.”

A key to thawing that middle is “getting managers to see that some of their actions are creating barriers to women in ways that they don’t intend,” says Dr. Correll, a sociology and organizational-behavior professor who directs Stanford’s Clayman Institute for Gender Research. But it won’t be easy, in part due to the polarized views of the workplace. Some 86% of men said that women have as many or more opportunities than men do. Far fewer women—57%—agreed.

Cloud-computing giant Salesforce. com is two years into a companywide “women’s surge” in which managers must consider women when filling open positions at the vice-president level and above; examine salaries for every role in the company to ensure women and men are paid equally; and ensure that women make up at least 30% of attendees at management summits or onstage roles at keynote presentations.

“We are in unexplored territory,” says CEO Marc Benioff, adding that he thinks fellow CEOs must push the issue to the forefront to meaningfully advance women. He allows there’s still not much of a road map—at least not yet. “When you go through business school, there are no classes in women’s leadership,” he says.

Gracia Martore, chief executive of Tegna Inc., says many companies would rather “pay lip service” to gender diversity than hold bosses accountable. Tegna is the broadcasting and digital-media company that remained after the spinoff of Gannett Co. ’s publishing arm earlier this year.

A lot of businesses go through the motions of listening to their female staffers, says Ms. Martore, who rose through Gannett management and served as its chief before the split. “I am not sure those women see the tangible steps that are being taken to put the money and the resources of the organization where their mouth is.’’ Ms. Martore ties managers’ pay packages to how well they recruit and promote women, and two of the company’s top six leaders are female.

One area of focus is pushing more women toward roles that matter to the company’s bottom line. So-called line roles lead more directly to the C-suite, Lean In and McKinsey found, but senior women are still more likely than men to be found in staff positions, such as human resources, legal affairs, information services and public relations.

While a majority of women hold line roles early in their careers, most occupy staff roles when they reach the VP level, typically the first rung of executive ranks. That’s true for 52% of women, compared with 39% of men, the Lean In and McKinsey study found. This scarcity of women in senior management line posts is especially stark in tech. About 9% of women have C-suite line positions in that industry.

Some companies are trying to attract more women to those jobs. At insurer Prudential Financial Inc., Judy Rice has worked to educate female colleagues about line roles since she became executive vice president and chief diversity officer of Prudential’s asset-management unit in January 2013. Ms. Rice, who spent eight years running the company’s mutual-fund business, observed that midlevel women hesitated to seek high-level jobs due to their lack of profit-and-loss experience. “If they feel they don’t have that one attribute, it won’t give them the confidence to raise their hand and go after that leadership role,’’ she says.

In June, Ms. Rice held a six-hour training session about line responsibilities for more than 175 middle managers, both male and female.

Rosalind Hudnell is trying to fix such disparities at Intel Corp. , where she is the chief diversity officer and VP for human resources, managing the chip maker’s $300 million plan to address diversity in tech. “We move people around,” she says. “It’s not like people get stuck in a so-called staff role.’’

Intel operates a sponsorship program to catapult more women into senior leadership, which usually requires P&L responsibilities. Sponsors are senior players who open the doors to promotions and push their protégé through. By contrast, mentors typically offer informal advice. High-level female executives at Intel have identified and sponsored junior women, offering practical tips about the need to replace underperformers rather than do those lieutenants’ work, for example. “Our job is to sponsor that woman until she becomes a VP,” Ms. Hudnell says.

Seventy-seven of its 394 VPs are women, compared with 27 of 141 in 2011.

Companies may need to do better PR for life at the top. Women, along with many men, cited stress and pressure associated with upper-management jobs as the main reason they didn’t aspire to those roles, a result that held whether the respondents were parents or not. And just 28% of senior-level women said they’re very happy with their career, compared with 40% of senior men. (The gender gap in career satisfaction was much narrower below the highest level.)

Such perceptions inspired Prudential’s Ms. Rice to hold an event last year designed to smash myths about the demands of senior leadership roles. Women at the VP level and above in asset management heard from three female CEOs of Prudential units. Some of those executives described how they occasionally left early to attend a child’s baseball game, then worked from home later that evening, Ms. Rice recollects.

Yet advancement through flexible work arrangements seems out of reach for many. Most companies canvassed by Lean In and McKinsey offer flexibility and career-development programs, but participation is low, as employees fear being penalized. “More than 90% of women and men believe taking extended family leave will hurt their position at work,” the study stated.

That observation is hardly new. The Families and Work Institute has monitored worker attitudes toward flexibility benefits for years, and has never seen a decrease in the percentage of employees saying “working flexibility will damage their careers,” reports Anne Weisberg, the New York group’s senior vice president for strategy.

Fueling the ambition gap may be the current culture of work, one which does no favors for men or women, and one in which fealty to work is all—at all hours—as caregiving and family life are shunted to the margins.

Worries about balancing work and family life rank among the biggest deterrents for both men and women in aiming for an executive role.

“There’s no such thing as work-life balance. There’s only life,” says veteran Microsoft Corp. executive Julie Larson-Green, who oversees hundreds of employees and leads design and user experience for Office 365 and Bing, among others. The software giant, which has expanded parental leave for both genders and mentorship programs for women, was recently named in a proposed class-action suit alleging managers unfairly passed over women for raises and promotions; Microsoft says it is reviewing the complaint.

Ms. Larson-Green advises her high performers to view careers as a long arc—no single moment is make or break, she says, so they can take a six-month maternity leave or, in the case of a male employee whose children travel the country to play soccer, take Fridays off much of the year.

She recalls another employee who requested a remote work assignment because the woman’s fiancé lived out-of-state. Colleagues advised against trying to keep the woman, saying that she would soon leave the company anyway. Ms. Larson-Green found a role that fit the woman’s skills; she stayed, eventually moved back to Seattle with her spouse, and now holds a key role on the Windows team.

Some view these arrangements as a “gamble,” but Ms. Larson-Green says the employees grow, and more important, stay with the company. “That’s a good trade for me.”

PwC LLP, the U.S. arm of a global professional-services firm, came up with a different strategy to reduce fears about taking family time. It exempts new mothers and anyone else off work for at least 16 weeks from being measured against their peers for their performance review that year.

Before 2010, “if you didn’t work a full year, it was very hard to get the top [performance] ranking,” remembers Jennifer Allyn, the firm’s diversity-strategy leader. A lowered rating hurt the chances that high performers returning from long maternity leaves would become PwC partners. “They were the pipeline for partnership,’’ she says. “I wanted to make sure that their ambition and career momentum were a constant.”

Under the revamped policy, staffers with protracted time off get performance reviews but no longer find themselves compared with colleagues who remained on the job. The shift had a dramatic impact on retention of new mothers. Last year, 98% of PwC women on maternity leave resumed work—up from 88% in 2009, Ms. Allyn reports. She thinks the increase reflects the women’s realization that their careers are still on track.

Ms. Waller is The Wall Street Journal’s bureau chief for management coverage and Ms. Lublin is its management news editor, both in New York. They can be reached at nikki.waller@wsj.com and joann.lublin@wsj.com.