Washington-area housing administrators said yesterday that new housing guidelines backed by the Reagan administration could cause the supply and quality of federal housing here to decline sharply.

A spokesman at the U.S. Department of Housing and Urban Development said the revised policies -- which require tenants in subsidized housing to pay a larger share of their incomes for rent and to earn less to qualify -- was intended to help the "truly needy" and to weed out all other families.

But housing experts from Montgomery, Arlington and Fairfax counties said in a briefing at the Metropolitan Washington Council of Governments that higher concentrations of poor tenants will bring higher maintenance costs and increase social backlash against subsidized housing.

"We're caught between the budget cuts and the new guidelines," said Mike Nail, chief of housing resources in Montgomery County, which operates 1,820 units of public housing. "We have 9,500 applicants on our waiting list for public housing. But the chance that we are going to be able to build any more public housing units in Montgomery County looks grim."

Nail said that housing subsidies paid to the county will drop over the next five years from $765,942 this year to only $335,474 in 1986.

"Our most optimistic projections would result in only 59 new public housing units being built in the next year and no units at all to be built after that," Nail reported to COG's housing committee.

Mike Scheurer of the Fairfax County Public Housing Authority said that as a result of revenues lost under the new housing policies, his agency expects deficits over the next three years to increase from a projected $35,558 this year to nearly $74,000 in 1984.

Maintenance will be the first item reduced, said Scheurer, whose agency operates 502 public housing units. "Unfortunately, many times the key to quality public housing lies in the very item to be cut," said Scheurer. "As the age of projects increase, the amount of maintenance also increases."

Virginia Peters, of the nonprofit, church-sponsored Wesley Housing Development Corp., which operates the 128-unit Strawbridge Square development in Lincolnia, said new guidelines will create negative attitudes toward federally subsidized housing.

"We will now have to break our promise to a community which was told that we would maintain an intercultural, interracial, and economically mixed group of tenants," Peters said.

"Now they find out that the development is largely going to be mostly low-income families," she added. "You go back to thoughts that maybe we're about to create the same kinds of disasters that existed in the projects that we tore down years ago."

Under the new guidelines, some 23 families living in Arlington's 77-unit View Terrace are no longer qualified to remain there. Cecilia Cassidy of the Arlington Housing Corp., a private housing agency, said that roughly 40 percent of the current residents in the complex eventually must be relocated at a projected cost of more than $100,000.

"We recognize there is a valid concern about the impact of the new housing policies," said W. Calvert Brand, HUD's deputy assistant secretary for policy and budget in housing. "But we believe that predictions of the negative effects of the guidelines are premature.

"Our judgment is that there really isn't a serious problem," Brand added. "We've found that number of families made ineligible under the new rules is so small that it is not likely that anyone will have to be displaced because of the new regulations."

However large or small the number, representatives of the local housing authorities say they are waiting for rules from the federal government on how quickly the newly ineligible residents must be moved.

Later this spring, the human resources office of COG said it would evaluate the impact of the government-required moves.