Men outnumbered women more than six-to-one last year in top jobs at U.S. corporations, where the rate of growth in the number of women filling the most powerful positions has slowed, an advocacy group reported on Wednesday.

At the current pace, women will reach parity with men in America's top corporate jobs in 40 years, said the study by Catalyst, a nonprofit research group in New York that promotes opportunities for women in business.

The study looked at women in top positions at Fortune 500 companies, the largest publicly traded firms based in the United States.

It found women held 16 percent of the highest U.S. corporate officer jobs in 2005, growing 0.23 percentage points a year since 2002, the last time Catalyst conducted a comparable study.

The growth rate from 2002 to 2005 was dramatically lower than the growth rate of 0.82 percentage points a year between 1995 and 2005, Catalyst said.

Catalyst President Ilene Lang called the pace disappointing. "The progress is very, very slow," she said in a telephone interview.

Research found women are excluded from top jobs largely due to three factors — gender-based stereotyping, exclusion from informal networks and a lack of role models, she said.

"Our research shows that women have similar ambitions to men and pursue the same success strategies as men but face different barriers," Lang said. "Women face barriers that men don't encounter."

Lang said a contributing factor may be that the number of top corporate jobs overall declined 20.5 percent between 2002 and 2005, and corporations have reduced hierarchies.

Also, companies may be satisfied with a "token" woman at the top, she said.

"There are plenty of people who say, 'Oh, we have one. We have enough. We just need our woman,"' she said. "That very much playing by the numbers, and it's tokenism."

The study found the average Fortune 500 company had 21.8 corporate officers, of whom an average 3.6 were women. More than half of had fewer than three women corporate officers.

In other findings, the study said women held 9.4 percent of so-called clout titles at U.S. corporations — titles higher than vice president — up from 7.9 percent in 2002.

Eight Fortune 500 companies were headed by a female chief executive, up from six in 2002. None was among the top 100 companies.

These rates come against a backdrop showing that women comprised 50.6 percent of the managerial and professional work force in 2005, and women earned 32 percent of the MBA degrees that year, Catalyst said.