When Irene Cohen, 83, learned that her health maintenance organization was planning to triple her monthly premiums and reduce her benefits, she telephoned a little-known Washington-based health group for help in fighting the proposal.

The call from Cohen, along with protests from several other seniors, helped spark a series of actions that led to the restoration of several important benefits for 1,300 senior citizens. It also marked the beginning of a new activism by the United Seniors Health Cooperative, an unusual organization for the growing numbers of elderly people.

"The feeling at United Seniors is that we can have a positive effect on health care problems in the Washington area . . . that we can be an advocate for our members," said Hanita Schreiber, director of member services.

Founded as an independent nonprofit group to provide information and advice that would help older residents negotiate the increasingly complicated and confusing health care system, United Seniors is the only consumer health cooperative of its kind in the country, according to James P. Firman, chief executive officer.

Among the founding board members, Firman said, are Arthur Flemming, former U.S. secretary of health, education and welfare; Esther Peterson, consumer adviser to Presidents Johnson and Carter, and T. Franklin Williams, director of the National Institute on Aging.

Since United Seniors began operating in March 1986, an estimated 7,700 elderly people and their families have joined, thereby becoming both the owners of the organization and the beneficiaries of its services, Firman said.

Basic services for members include a monthly newsletter on Medicare and insurance benefits, publications dealing with other issues, answers to questions about Medicare coverage and reimbursement, listings of about 50 public and private financial assistance programs for which members may be eligible, names of physicians who accept Medicare assignments, a "hospital kit" that provides information about patient rights, and discounts of 15 to 25 percent for home health services, eye care, hearing aids, podiatry services and medical equipment and supplies.

Members pay annual fees of $5 per person or $7.50 per couple. Additional services are available to members for additional fees. For example, a member can order a computerized "medigap check-up" to find out how Medicare supplemental insurance coverage compares with another policy. The fee for this service is $15.

Last week, the board of directors voted to expand membership services to include advocacy on behalf of members in health care issues.

"We don't see ourselves as the Gray Panthers," Schreiber said. "They are a more militant group . . . . I don't see us taking to the street and demonstrating."

Nor does United Seniors aspire to play the kind of advocacy role that has been adopted by other groups such as the American Association of Retired Persons, Schreiber said.

"We are local and the AARP is national," Schreiber said. "We concentrate completely on health care whereas AARP deals with many issues. And the third thing is we don't sell insurance and AARP does."

United Seniors' decision to become more active in advocating senior interests was applauded by other officials in the field of aging. They said that there is a greater need for advocacy because of the aging of the population and the increasingly complex array of health and social service regulations.

"We are glad to have them emerge as a colleague," said Eric Friedman, an investigator for the Montgomery County Office of Consumer Affairs and the leader in the recent negotiations with the M.D.-Individual Practice Association, the health maintenance organization to which Cohen belongs.

Friedman said his agency "had the access and the power to get M.D.-IPA to sit down at a negotiating table, under threat of county action."

But it was Schreiber, representing members of United Seniors, who came up with a recommendation for a settlement with M.D.-IPA, Friedman said. Essentially, Schreiber agreed to the rate increase with the condition that M.D.-IPA restore several benefits, including partial reimbursement for pharmacy purchases.

Schreiber said she based her recommendation on interviews with several seniors about their needs and on information from the United Seniors' data base on Medicare supplementary coverage.

"United Seniors served a very important role in advocating a position and providing information for that position," Friedman said.

Joseph L. Guarriello, vice president of corporate affairs for M.D.-IPA, described Schreiber as "a catalyst in solving the problem" because she was "very knowledgeable and very reasonable to work with."

After M.D.-IPA agreed to restore pharmacy, hospital admission and several other key benefits, Friedman and Schreiber withdrew their opposition to the rate increase. The changes in the M.D.-IPA rates and benefits are scheduled to take effect Feb. 1.