America’s global rank in college completion among young adults is slipping, according to a report released Tuesday, signaling that the higher education ambitions of other nations are progressing at a swifter pace.

The analysis comes two years after President Obama sought to stir the nation’s competitive spirit with a pledge to retake the lead by 2020.

Instead of gaining ground, the United States has fallen from 12th to 16th in the share of adults age 25 to 34 holding degrees, according to the report from the Organization for Economic Cooperation and Development. It trails global leaders South Korea, Canada and Japan and is mired in the middle of the pack among developed nations.

The stagnant U.S. performance on this key international benchmark reflects at least two trends: the rapid expansion of college attendance in Asia and Europe, and the continuing emphasis on four-year degrees in the United States while other nations focus far more on one- and two-year professional credentials.

“Most of these countries are moving ahead,” said Jamie Merisotis, chief executive of the Lumina Foundation, an advocate of higher education reform. “And we are stuck in neutral.”

Obama’s pledge challenged a society generally presumed to have the world’s best higher education system. The United States ranks second, after Norway, in share of adults age 25 to 64 with bachelor’s degrees. Top U.S. universities perennially draw huge numbers of foreign students.

But U.S. officials say it is crucial for as many young adults as possible to get a college degree of any sort to help the nation compete in the global economy. When the president announced his goal in July 2009 at a community college in Warren, Mich., the United States ranked 12th among 36 developed nations in the share of young adults with degrees. The college attainment rate for young adults, as the measure is known, was 39 percent. The figures Obama relied on were based on 2006 data.

Tuesday’s report, based on 2009 data, showed the comparable attainment rate has crept up to 41 percent. But in South Korea, which has become the world leader, the rate has reached 63 percent. Canada and Japan rank second and third, respectively, with attainments of about 56 percent.

The United States trails Russia, Ireland, Norway, New Zealand, Australia, Denmark, Israel and Belgium — as well as Luxembourg, the United Kingdom, France and Sweden, which all passed America in the latest ranking.

“We don’t have any evidence that anything is getting worse in the United States,” said Andreas Schleicher, head of the Indicators and Analysis Division of the OECD in Paris. “It is just that there is a great deal of dynamism all over the world, and many countries are catching up.”

The United States last led the world in college attainment of young adults in the 1970s. Could the nation regain the lead by 2020? The numbers are against it.

From 1998 to 2009, the share of young American adults with college degrees rose 5 percentage points. But Japan’s attainment rate rose 11 points in those years, and Canada’s rose 10 points. In the global horse race, those countries aren’t just in the lead; they’re pulling away.

College attainment is soaring in China and India as well, although both nations lag far behind the United States, and the OECD has not consistently tracked them. China produces the largest number of new college students.

“I think our country just got complacent. We got self-satisfied,” said Arne Duncan, the U.S. education secretary. “I use these stats everywhere we go, and people are mostly stunned.”

Duncan contends that Obama’s goal is realistic. Half of all states, he said, have set “real targets” for raising college completion. And hundreds of universities have embraced Obama’s quest, setting an unofficial industry-wide target of 60 percent attainment by 2020.

But even that benchmark is problematic: South Korea has topped it.

Obama focused much of his initiative on community colleges. The two-year schools enroll nearly two-fifths of all U.S. college students, but their overall graduation rate is 21 percent.

To raise that performance, the president proposed $12 billion to improve two-year colleges and expand their capacity. Congress approved $2 billion.

In framing his challenge to the nation, Obama and his aides seized on a relatively unflattering chart within an OECD report. It compared nations according to the share of young adults who hold any type of college degree, including short-duration professional degrees.

The United States looked bad on that chart partly because of its historic focus on the bachelor’s degree. Nations that did well emphasized shorter-term professional degrees.

The United States fares much better in rankings that consider the full adult population. Older Americans have much higher college attainment rates than those who are younger. The attainment rate for younger adults is hindered by a growing population of immigrants from families without a tradition of college attendance. Many of America’s economic rivals, by contrast, are smaller, homo­genous nations with shrinking populations.

The best U.S. universities are still the best in the world. U.S. schools claimed the top five spots on the 2010 Times Higher Education World University Rankings, and 18 of the top 25. The best-placed Canadian, Chinese and Japanese institutions ranked 17th, 21st and 26th, respectively.

Overall, graduation rates in U.S. colleges are rising, slowly — but not in community colleges. The public two-year campuses are over-enrolled, courses are oversubscribed and students take ever longer to finish.

Some economists say America should reorder its priorities to stress short-term professional degrees and certificate programs alongside baccalaureate degrees. That, they say, was the clear message from Obama when he challenged every American to commit to one more year of higher education or job training — not four more years.

“He was trying to say to people, ‘You don’t need to get a BA,’ ” said Anthony Carnevale, director of the Georgetown University Center on Education and the Workforce. “He was saying, ‘You need a degree with labor-market value.’ ”

The link between level of degree and earnings has broken down, Carnevale said. Years of education matter less, and field of study matters more. Canada, Japan and many European nations were quick to recognize that change and have organized around delivering associate-level degrees. U.S. community colleges, by contrast, devote much of their energy to preparing students for transfer to four-year colleges.

Many students leave college without any degree. That, said Merisotis, of the Lumina Foundation, is why “37 million Americans have gone to college and have nothing to show for it.”