Women working for the federal government earn less than men overall but the gap is shrinking, and most of the difference is the result of women being concentrated in lower-paying jobs with too few occupying the top ranks, a government report issued Friday found.

The Office of Personnel Management’s study showed an overall gender pay gap for white-collar occupations of 12.7 percent in 2012, down from 19.8 percent in 2002 and 30 percent in 1992.

“According to our comprehensive, in-depth review of 37 white-collar Federal job categories, in 2012, women were paid 87 cents for every dollar that a man was paid,” OPM Director Katherine Archuleta said on the agency’s Web site. “In 1992, women in the Federal workforce made just 70 cents on the dollar.”

The report noted, however, that “differences in the distribution of males and females across occupational categories appear to explain much of the pay gap.”

The OPM study — which shows significant progress over 20 years, while acknowledging there’s more work to do — is also ripe for political cherry-picking by conservatives who argue that gender pay equity is disappearing and that Democrats have raised the issue to mobilize women for the November midterm elections. That debate was center stage last week.

On Tuesday, President Obama signed two executive orders, one that requires government contractors to report on salaries by gender and another that bars them from punishing employees who discuss salaries among themselves — a move that drew advocates’ praise and conservatives’ protests. On Wednesday, the Senate put a fine point on the controversy when it failed by six votes to pass the Paycheck Fairness Act, which would have strengthened employee protections under the Equal Pay Act.

The raw pay-gap number for the federal workforce falls below the 23 percent figure that the White House and some outside groups use as the overall difference between male and female salaries, a figure that others criticize for not taking into account differences such as work experience and hours of work.

OPM said that although its study “shows that some portion of the male-female pay gap is unexplained — that is, not explained by the factors included in our analysis — that does not mean that the unexplained gap is necessarily attributable to discrimination.”

Yet, OPM did not shy away from highlighting some entrenched and frustrating realities for women in government. It found, for example, that agencies use special authorities to set higher starting salaries when hiring men than when hiring women.

In a blog post, Archuleta said that while the report “shows the progress that we’ve made, we won’t be satisfied until women working in federal jobs earn the same as their male counterparts, at every level. That’s why our report also lays out a road map for how we can continue to address this pay disparity.

“For starters, we need to address the imbalance of hiring in all occupations. We need to build stronger pipelines for women across the board,” she said. “We also must improve the transparency of our pay tables, particularly when it comes to starting salaries for women, which tend to lag behind men’s.”

Still, some of the disparity is based on occupation, the report said, adding that women receive promotions and performance-based increases slightly more frequently.

Other factors that may be contributing to the pay gap include work experience, caregiving responsibilities, motivation and performance, OPM said. However, the agency said, “To the extent that the explaining factors are subject to employee or employer control, some unknown portion of the explained gap may reflect the effects of discrimination (either societal or employer-specific).”

Romina Boccia, a policy analyst with the Heritage Foundation, said that some of the report’s data support conservative arguments that the wage gap is shrinking and that much of the remaining disparity is because of factors beyond discrimination.

“The report’s findings show that once key factors such as occupation, education, and length of service are taken into account, the wage gap in the federal workforce all but disappears,” Boccia said in a statement. “The same applies to the economy-wide gender pay gap.”

Stephanie Jaros, a social scientist for the Department of Homeland Security, wasn’t debating Friday whether a pay gap exists, but she said she has not had to confront one in the federal ranks. She credits the government’s structured pay system and the fact that its salary rates are public information.

“Part of the reason for the pay gap in the private sector is that salaries are not transparent,” she said. “Transparency allows communication, so people would know about disparity much quicker in the federal government.”

OPM’s report also said that the narrowing pay gap reflects the changing nature of federal employment: a shift away from occupations such as low-paying clerical jobs, disproportionately filled by women, and growth in higher-paying professional and administrative jobs that are increasingly held by women — 68 percent of federally employed white-collar women are now in those fields, compared with 45 percent in 1992.

The portion of the federal workforce in clerical positions dropped by two-thirds, to 5.3 percent, during that time, while professional and administrative positions made up 71.9 percent, up from 59.2 percent.

Women remain the majority of clerical workers, however, at 69 percent, compared with their 46 percent share in the overall federal workforce.

The report also found that the raw gap is smaller at higher-paying levels. For supervisors and managers, it’s 4.4 percent, and among senior executives it’s less than 1 percent.

But women make up only about a third of employees at those higher leadership levels, and are underrepresented in higher-paying science, technology, engineering and mathematics fields.

“Personally, I feel like I could have gone further, but I’m fortunate to be employed by a terrific agency,” said Pamela Jones, a 50-year-old Justice Department analyst from Arlington. Jones added that she thinks pay gaps affect minorities as well as women.

The raw gap varied by age, from 5 percent for those 25 to 34 to 17 percent for those 55 to 64.

After occupation, education was the second-largest factor helping to explain the gap, but it is growing less significant as women’s average education levels increase, the report said.

As part of a “roadmap” forward, Archuleta issued a memo to agencies telling them to collect data on occupations in terms of grade patterns by gender, review how they classify jobs for pay-setting and publicly post the salary rates of agency-specific pay systems, among other steps.

OPM said it will clarify pay-setting flexibilities and share best practices on setting starting salaries in gender-neutral ways, and will develop recruitment strategies for increasing women in occupations and higher levels where they are underrepresented.

Janet Kopenhaver, Washington representative for Federally Employed Women, said that althought the government’s efforts are appreciated, her nonprofit advocacy group is more concerned about the inability of women to be adequately represented at the senior levels.

“Women face many hurdles in getting into the higher-paying jobs,” she said, adding that mentoring programs and other initiatives are necessary to help women advance.

“That is why FEW has been working so hard with OPM and the administration to get them to do something about the serious demise of the Federal Women’s Program in federal agencies. . . . That is why we are a little disappointed that in the OPM report just released, no mention is included in the recommendations section of revamping these offices.”

Joe Davidson and Josh Hicks contributed to this report.