The D.C. Human Rights Office, holding that anyone who receives a business license from the District government must comply with the city's antidiscrimination law, has found "probable cause to believe" that the all-male Cosmos Club violates the law by barring women as members.

The ruling, if sustained, apparently would sharply limit the ability of organizations to exclude people from membership on the basis of sex, race and other factors, and would be far broader in its application than an antidiscrimination bill passed in September by the D.C. Council.

The sweeping decision is the latest development in a long-running conflict over men-only clubs in the District, and arises out of a two-pronged strategy by opponents of the clubs who also sought the council legislation.

In the ruling, Maudine R. Cooper, head of the city's rights agency, directed the prestigious club to try to reach a conciliation agreement in 30 days to change its 109-year-old policy of admitting only men.

If the club, whose members include a Supreme Court justice, two U.S. senators and D.C.'s former mayor, does not make the change, Cooper said she will refer the case for a public hearing to the 15-member D.C. Human Rights Commission, which can issue a final ruling.

John F. Banzhaf III, a law professor at George Washington University who brought the case against the club along with Teresa Schwartz, another GW law professor, said the ruling means that the club may lose its liquor license if it does not let women become members. He urged the club to settle the case rather than ask for a "costly and embarrassing" hearing.

John R. Risher Jr., the club's attorney, said the Cosmos Club "has not decided yet what it's going to do. It's not the simplest matter to deal with."

Risher, a former D.C. corporation counsel, said that using the city's licensing power to change the policies of private clubs is "plainly wrong." He added, "I've got a lot of very good constitutional company in feeling strongly that one of the most important things our constitution guarantees is private association."

The city's wide-ranging 1977 Human Rights Act bars discrimination on the basis of sex, race and 14 other categories, including age, marital status, religion, sexual orientation, personal appearance, "matriculation," source of income and place of residence or business. Cooper's ruling would apply such prohibitions to any organization that holds a city license, occupancy permit, franchise or special exemption -- even if such an organization were "distinctly private."

Religious and political groups can choose members of the same "persuasion," but they cannot discriminate on other grounds, Banzhaf said.

In an interview, Cooper declared, "You can associate with anyone you want in your basement. Once you get a license or a city benefit, you come under the law."

In late September, the council amended the antidiscrimination law to cover explicitly the city's major private clubs -- extending the act to include any club with at least 350 members that regularly serves meals and receives payment from nonmembers for use of its facilities for business purposes. The amendment was signed by Mayor Marion Barry on Oct. 16 and will take effect, unless Congress rejects it, after a 30-day congressional review period.

In her decision, Cooper said the club is doubly bound by the rights act because it is not the type of "distinctly private" organization that the law partially exempts.

Cooper said that with more than 3,200 members, the club is too large and nonselective to be "distinctly private." She said it also earned over $300,000 in 1985 by allowing nonmembers to hold meetings and rent rooms in its clubhouse at 2121 Massachusetts Ave. NW.

In a statement submitted to the human rights office, the club contended that its membership policy is "highly selective, accepting as members only men who have distinguished themselves in science, literature, the learned professions or public service."

Since early 1986, the ADA and other liberal and feminist groups have been seeking to have the Cosmos Club's liquor license revoked on the grounds of discrimination. But the District's Alcoholic Beverage Control Board has indicated that it would not rule on the protest until the Human Rights Office made a determination. Banzhaf and Schwartz filed their complaint with the human rights agency in July 1986.

Yesterday Roberta Weiner, a member of ADA's executive board, said the ADA sought new council legislation because of uncertainty about how long it would take for the rights agency to rule on the complaint and "how good a ruling it would be." The organization has been attacking men's clubs in cities across the country.