This week's bipartisan budget agreement proposes the biggest cutback ever in veterans' housing benefits by restricting their eligibility for home loan guarantees to the first 10 years after they leave military service.

Congressional and administration budget leaders said the cutback is one of several ways they devised to trim housing finance programs to help meet the deficit-reduction target of $500 billion over the next five years.

Other proposals would raise fees veterans pay for a government-guaranteed home loan and make changes in the way the Department of Veterans Affairs handles foreclosures on guaranteed mortgages.

Low-income housing tax credits would be extended for a year, but no funds for mortgage revenue bonds were provided in the agreement. The bonds, sold by state and local governments, provide money to help moderate-income families buy their first homes.

Under the budget agreement, Congress's tax-writing committees can make changes in some programs as long as spending or savings goals are met, but many others must be included in legislation.

The 10-year limit on veterans' eligibility for loan guarantees is likely to meet heavy opposition in Congress, according to a spokeswoman for the House Committee on Veterans Affairs. The budget agreement said the VA must bring in $620 million over the next five years to help trim the nation's deficit.

Committee members are unlikely to approve legislation that would bar veterans from the nation's most recent war, in Vietnam, from getting VA housing loans, she said. Instead, they are likely to meet the savings target by making smaller cuts in many programs.

In another proposed change, the mortgage-guarantee fee charged to veterans would be increased from 1.25 percent of the loan amount to 1.75 percent. Veterans paid no fees until Congress approved the 1.25 percent charge last November as part of a major restructuring of the loan fund. The money goes into a mortgage indemnity fund to reimburse the VA for paying off loans when veterans default.

Private lenders complained this week that the proposed changes in the formula VA uses to dispose of properties when defaults occur will result in millions of dollars in losses to lending institutions.

Congress focused attention on VA programs because of heavy losses that have required $2.2 billion in appropriations since 1984 to keep the loan guaranty fund solvent.

Sen. Frank H. Murkowski (R-Alaska), the ranking Republican on the Senate Committee on Veterans Affairs, said the VA's loan programs "need to be reexamined" and Congress should decide how to turn it into a "realistically self-funding" program.

While ordering savings at the VA, congressional and administration leaders decided to assume millions of dollars in losses in order to fund low-income housing construction.

Low-income housing tax credits would be extended for a year and allocated to state housing agencies at a level of $1.25 per state resident under the agreement.

The credits provide tax breaks for private builders and investors. The government's losses would be $200 million next year and would rise to $1.7 billion in 1995 if Congress continues to renew the program each year, according to the budget summit's estimates.

The building industry and some low-income housing groups hoped for permanent authorization for the credits, which have been the principal source of private money for new housing since the 1986 tax law eliminated nearly all other tax breaks designed to raise money for low-income housing construction.

As a result, the tax credits "are absolutely essential" for building new low-income housing, said Michael A. Stegman, chairman of the Department of City and Regional Planning at the University of North Carolina.

But "it is clear they are very complicated to use, they are expensive and they are inadequate by themselves to create low-income housing," he said. About three-quarters of all the housing projects funded by tax credits must get other types of subsidies, usually from the federal government, to be successful, he said.

States' authority to issue mortgage revenue bonds for funding low-cost housing were eliminated altogether in the budget agreement. Local governments have been issuing the bonds for nearly 20 years, using the estimated $61 billion in bond sales to make more than 95,000 home loans to low- and moderate-income buyers, according to John McEvoy, executive vice president of the National Council of State Housing Agencies.

To qualify for the loans, buyers must have incomes equal to 115 percent of median incomes in the area where they live, and must be buying their first houses.

The current ceiling of $124,875 on the size of home mortgages the Federal Housing Administration can insure in high-cost areas of the country would become permanent under the budget agreement.

Insurance premium refunds to about 145,000 homeowners, who bought their houses before a 1982 change in the way FHA collected insurance premiums, would be canceled.

The refunds typically range from $900 to $1,000 and about 145,000 borrowers a year would lose out. Owners who bought their homes in 1983 and later years would not be affected.

The budget agreement also said the Department of Housing and Urban Development also must make changes to put the ailing single-family loan fund on a sound financial basis.