The number of group employee insurance plans that cover birth control pills and other contraceptives increased dramatically over the past decade, spurred by federal and state requirements, lawsuits demanding coverage and, apparently, Viagra.

In a comprehensive study to be released tomorrow, the Alan Guttmacher Institute found that 86 percent of employer-provided health plans covered a full range of contraceptive choices in 2002, compared with 28 percent in a parallel 1993 study.

"This is an enormous and exciting change," said Sharon Camp, president of the Guttmacher Institute, which studies issues of reproductive health. "Significant gaps still remain in contraception coverage, but the progress is a real untold success story."

Although legislative, legal and regulatory action spurred many health plans to change, Camp said, a less tangible but clearly important factor was the advent of Viagra. As soon as the male impotency drug was approved by the Food and Drug Administration in 1998, most employer health plans placed it on their list of covered drugs, setting off a torrent of criticism from women whose birth control needs often were not covered.

"At the time Viagra came out and was immediately covered, many health plans were still defining contraceptives as lifestyle drugs," Camp said. "The outrage that women felt was enormous and, we think, really drove the movement towards contraceptive equity."

The new study, published in the journal Perspectives on Sexual and Reproductive Health, estimates that 30 to 40 percent of the increase in plan coverage was directly tied to state mandates. Since 1998, when Maryland passed the nation's first law requiring employer health plans to cover contraceptives if they also offer prescription drug and device benefits, 20 other states have passed similar legislation.

Other official steps that expanded birth control coverage were the federal government's decision in 1999 to require contraceptive coverage in the Federal Employees Health Benefits Program and the finding in 2000 by the U.S. Equal Employment Opportunity Commission that failure of employers to include contraceptives in prescription drug coverage constitutes sex discrimination.

Susan Pisano, spokeswoman for the American Association of Health Plans, said the Guttmacher Institute's findings were consistent with her group's observations. She said the association supports any expansion of benefits freely decided upon by an employer, but it opposes legislative or regulatory mandates.

"The cumulative effect of mandates has been to make insurance for some employers too expensive to afford," she said. "We think employers need to be in position to tailor their benefit packages to address what they want for their employees."

She also said coverage of new products inevitably increases costs paid by the employer, the employees or both.

The new report came from a sampling of 205 health care insurers. The authors of the report, Adam Sonfield and Rachel Benson Gold, said too little information was available from employers who self-insure, typically large companies, to be meaningful. About half of all employee benefit plans are administered by the companies themselves and are not subject to the state coverage mandates.

Nonetheless, Camp said she believes many self-insured plans also have begun to offer contraceptive coverage. She said three recent lawsuits, involving Dow Jones & Co., DaimlerChrysler and the Bartell Drug Co., all led to the companies adding contraceptive coverage.

"People in industry are beginning to wake up to the fact that providing contraceptive coverage is in their employees' interests and in their interest, too," Camp said. Nonetheless, legislative mandates clearly play an important role: The study found that about 90 percent of plans in states with mandates provide the five leading prescription contraceptives, while only about half of plans in non-mandate states do.

Although the number of health plans providing comprehensive coverage has increased, another new survey, sponsored by the Association of Reproductive Health Professionals, the Black Women's Health Imperative and the Planned Parenthood Federation of America, showed that new methods of contraception, including rings and patches, are slow to receive coverage.

The study found that more than 80 percent of insurance companies cover oral contraceptives, an older form of birth control, but only 40 to 50 percent of companies cover the newer methods.