Mayors from cities that have sizable homosexual populations today urged the federal government to provide guaranteed medical care to victims of Acquired Immune Deficiency Syndrome (AIDS), a deadly new disease that strikes mainly at homosexual men.

San Francisco's Dianne Feinstein, New York's Edward I. Koch, New Orleans' Ernest N. Morial and D.C. Mayor Marion Barry, representing cities with politically active homosexual communities, won preliminary approval of a resolution calling for "government assurance of adequate medical, hospital and hospice care and housing for victims of AIDS." The resolution also calls for more federal and local funding for research into the causes of and possible cure for AIDS, which are now unknown.

The AIDS resolution was one of about 35 adopted today, over the objections of the Reagan administration, by an executive committee at the annual four-day meeting of the U.S. Conference of Mayors. On a 2-to-1 party-line vote, Democratic mayors pushed through another resolution calling on Congress to restrain military spending, postpone next month's 10 percent tax cut and use the savings for domestic needs.

The administration is dispatching three Cabinet members here--Transportation Secretary Elizabeth Hanford Dole, Health and Human Services Secretary Margaret M. Heckler and Housing and Urban Development Secretary Samuel R. Pierce Jr.--to help oppose most of the resolutions. An administration document being circulated here says that caring for AIDS victims is "the responsibility of state, local and private entities."

Feinstein called AIDS "a health emergency" that requires "a long-term federal fund commitment . . . . Each of us is on the front lines in this new war," she said.

"Washington certainly has its share of potential AIDS victims," Barry said. He said the federal response to the disease "has been hampered by the fact that it seems to be more prevalent in the homosexual community."

More than two-thirds of the 1,552 reported victims of AIDS in the nation have been homosexual or bisexual males with multiple sexual partners. Of these, more than 550 have died since the disease was first reported in June, 1981. Over months or years, AIDS progressively weakens a patient's immunological defenses against disease.

Jeffrey Coplan, assistant director of the federal Centers for Disease Control, said that AIDS "is certainly my No. 1 priority. It's the major disease currently being undertaken by the CDC," which he said has dispatched scientists to San Francisco, New York, Los Angeles and Miami.

But Roger Enlow, director of New York's Office of Gay and Lesbian Health, said, "I think we're falling behind at the city level. At the federal level, it's probably too little, too late."

Administration officials have their work cut out in opposing the rest of the conference's urban wish lists. For example, the mayors call for a $1 billion increase in community development and urban development grants, but the administration position paper says that would "seem excessive" and "would likely promote waste and an inefficient use of resources."

The mayors also are urging that health insurance be provided for the unemployed, but the administration says such a program "would escalate beyond affordable levels."

The administration also is opposing resolutions that call for construction subsidies for low-income housing, mass transit operating aid, continued regulation of some natural gas supplies, extension of tax-exempt mortgage revenue bonds, increased funding for hazardous waste cleanup, full funding of the food stamp program, advance notification of factory closings and creation of a $5 billion Reconstruction Finance Corp. These and other proposals will be voted on by the full conference on Wednesday.

In the debate over the tax cut and defense spending, Republican Mayor Richard Carver of Peoria, Ill., said the mayors had strayed beyond their area of expertise. "The mayors hurt themselves by making the Defense Department the whipping boys for why we aren't spending more on urban programs," he said. "I think a strong private economy is going to solve a great deal more problems than pumping money into cities through public expenditures."

But Democratic Mayor Joseph Sensenbrenner of Madison, Wis., said that "the need for increased funding for national defense must not overshadow the acute needs of our cities," including large-scale repair of roads and bridges.