Critics sharply disputed administration claims this week that public-housing modernization and the shelter needs of low-income Americans can be met despite the massive budget cuts it is recommending.

Much of the U.S. public housing stock is badly deteriorated, according to critics of the Reagan administration's housing program. They said the housing vouchers the Department of Housing and Urban Development has asked Congress for will be of no use to needy Americans in many cities where little rental housing they can afford is available.

The nation's 1.3 million public housing units, some of them built in the 1930s and 1940s, shelter about 4 million people. Leaders of the National Association of Housing and Redevelopment Officials (NAHRO) said public housing represents a $75 billion "national investment in a capital asset" but that administration policies pose a serious threat to it.

Money provided in recent years for operating expenses and modernization has been inadequate, with the result that "thousands of . . . units have fallen into disrepair as more and more routine maintenance has had to be deferred," according to NAHRO, whose members come from more than 2,200 local public housing and community development agencies.

HUD's 1987 budget proposals, announced this week, call for cutting off modernization funds for the next two years. Only $225 million would be provided for emergency repairs in fiscal year 1987. Meanwhile, all but $225 million of the $1.5 billion appropriated for modernization this year would be rescinded and that money would be used only for emergency repairs.

HUD Secretary Samuel R. Pierce Jr. said this week that public housing authorities have $2.7 billion in unspent modernization funds on hand, enough to continue the present pace of rehabilitation work without new appropriations for the next two years.

NAHRO President Melvin J. Adams disagreed, saying most of this $2.7 billion already has been committed to work that is not yet complete. Adams is director of the Metropolitan Dade County (Miami) Department of Housing and Urban Development. An additional problem is that "there never has been enough money" coming from HUD to enable local authorities to build up a reserve fund to cover repairs and replacement of equipment, he said.

Adams said more than 1,000 units of Miami public housing were built in the 1930s and have the original electrical wiring, which is inadequate, and the original plumbing, which is badly deteriorated. He said his housing authority has no uncommitted modernization funds.

HUD has asked for a total 1987 budget of $5.5 billion in spending authority, down from $15.8 billion that Congress appropiated in the current year. The cuts bite deeply into housing assistance funds and come at a time when people are doubling up in housing at a record rate and homelessness is increasing, according to critics.

Public housing waiting lists in many metropolitan areas contain thousands of applicants, according to NAHRO. Adams said 60,000 people are on the list in the Miami area and have to wait an average of 10 years.

The administration wants to limit new housing assistance for low-income families not currently in public housing to 50,000 vouchers in 1987. Under this system, families find their own homes on the private market and use the vouchers to pay a portion of the rent.

Critics say the vouchers are useless in areas of the country where rental housing is in short supply, which include many major cities.

James E. Baugh, HUD deputy assistant secretary for public and Indian housing, acknowledged that, "In tight markets . . . you obviously have a problem. Vouchers don't work at all on an Indian reservation."

He said, however, that studies show there is an ample supply of rental housing in the United States, prompting HUD to make vouchers "the centerpiece of our assisted housing policy."

In areas where the rental housing is scarce, however, HUD would expect local governments to use their budget surpluses, if they have them, or Community Development Block Grant money to house low-income people, another HUD spokesman said.

Congress has rejected many major cuts in housing budgets the administration has proposed in the past, and is expected to do the same this year. Some housing advocates fear, however, that pressures for spending cuts exerted by the Gramm-Rudman-Hollings deficit reduction act makes housing programs more vulnerable.

The housing and redevelopment officials' organization urged that housing aid be spared and that a tax increase be imposed, with the revenue it generates going directly to reduce the federal deficit.

HUD's 1987 budget requests and proposals to rescind $5.1 billion in the 1986 budget, nearly all of it for subsidized housing, and defer spending another $2.3 billion also raised the hackles of House Democrats, who called for Congress to express disapproval.

Rep. Henry B. Gonzalez (D-Tex.), chairman of the housing subcommittee of the House Banking, Finance and Urban Affairs Committee, said the cuts proposed by the administration "are merely arbitrary, even capricious. They're devices to deliver a budget that is in technical compliance with the Gramm-Rudman Act while . . . maintaining the myths of voodoo economics."

The administration has "weak justifications" for the cuts, according to Rep. Barney Frank (D-Mass.). "In fact, what we're getting here are cuts in programs that have already been more severely cut than any other element of the federal budget. . . . "

He said President Reagan is proposing increases in other areas of the federal budget, including foreign aid for the Philippines, "which means by the time he's through, if we adopt his budget, the only urban development program being financed by the American government will be Imelda Marcos' real estate purchases in midtown Manhattan."