WASHINGTON (AP) _ Two cities and a group of homeless advocates sued on Thursday to force the Census to recount the nation's street people.

In U.S. District Court, they charged that the Census Bureau deliberately failed to count thousands in its one-night tally of the homeless, in order to reduce the federal aid available to them.

The suit asks the government to admit that the 1990 Census is inaccurate and appoint a commission to develop a better method for a new count. They asked the court to let them nominate a majority of the commission members.

The suit was filed by the cities of Baltimore and San Francisco, the U.S. Conference of Mayors, 15 homeless advocacy organizations, seven homeless people and the National Law Center on Homelessness and Poverty, a nonprofit legal advocacy group.

Census spokeswoman Karen Wheeless said, ''Until we've seen what the suit specifically says, there's not a lot we can say.''

Census data is used to determine where $45 billion in federal funds from 97 programs is spent, the suit said. An undercount would serve ''to reduce the level of funding for programs which would benefit the homeless,'' the suit said.

In an interview, Joanne Selinske, director of the Mayor's Office of Homeless Services in Baltimore, said census takers missed hundreds of homeless people, despite the city's efforts to get them to places where they were certain to be counted.

''Large numbers of homeless people came out and waited for hours, and enumerators never showed up,'' she said. ''If the count is used to allocate federal money, a faulty count would result in misallocation.''

She estimated that Baltimore has 2,500 homeless people. The 1990 Census said it had 1,531 people.

Buck Delventhal, deputy city attorney in San Francisco, said, ''The homeless problem in this country is visited in a disproportionate fashion on the larger cities. When you have an undercount of the homeless, that adversely affects our ability to participate in entitlement programs.''

The law center said estimates of the homeless in San Francisco range from 8,000 to 10,000, but the Census counted only 5,569.

There are no firm numbers on how many homeless people the Census missed, but estimates range from 700,000 to 3 million, said Maria Foscarinis, an attorney for the law center, which prepared the suit.

''This is terribly important. The Census is the fundamental instrument for distribution of political power in this country,'' Ms. Foscarinis said.

The 1990 Census estimated the homeless population at 400,000. The estimate was taken from the March 20, 1990, ''Street and Shelter Night'' count of the homeless population. But only 5,050 of the country's 39,000 local governments participated in the count, the lawsuit said.

Among the places census takers did not check, the suit said, were rooftops, under tarps or inside cardboard structures, bushes, trees, cars, caves and trash bins. The Census Bureau's effort was inadequately funded and staffed, and census takers often were not provided with security needed to do their jobs, the suit said.

''The bureau was aware of the fact that, by excluding the hidden homeless, it would miss most homeless people,'' the suit said.

The suit estimated that 70 percent of the homeless in Los Angeles, 32 percent in New Orleans, 47 percent in New York City and 69 percent in Phoenix were not counted.