The Reagan administration, backed by the General Accounting Office, yesterday assailed mortgage revenue bonds as an "unneeded" and "inefficient" subsidy to home buyers that should be allowed to expire as scheduled at the end of the year.

"We believe that federal support for owner-occupied housing for low- and moderate-income families is sufficient without continuation of this program," John E. Chapoton, assistant Treasury secretary for tax policy, told a Senate Finance subcommittee.

He estimated that, if the program is renewed for three years, the total cost to the federal Treasury could reach $15 billion.

But the panel had other ideas. "It seems to me that we have a program that is working, a program that is effective," said Sen. William V. Roth Jr. (R-Del.). "The administration must recognize that renewal is legislation that is going to succeed."

Mortgage revenue bonds are a device that became very popular in the late 1970s for providing home buyers with below-market mortgage loans.

States or localities use their authority to float tax-exempt bonds, which generally command lower rates in the bond market. Then they lend the money to home buyers at reduced rates, which allows more people to qualify for loans, particularly when interest rates are high in the conventional market.

In 1980, Congress imposed some restrictions on the program, notably limiting it to first-time home buyers, but its popularity has continued to grow.

By the end of this year, there will be $39.4 billion in these bonds outstanding, Congressional Budget Office Director Alice M. Rivlin testified.

Now, faced with the Dec. 31 "sunset" of the law allowing the bonds, states, localities and various real estate trade groups have mounted a major campaign for renewal. So far, according to the Council of State Housing Agencies, the Senate renewal bill, sponsored by Roth and George J. Mitchell (D-Maine), has accumulated 74 cosponsors, while the House version, offered by Reps. Thomas J. Downey (D-N.Y.) and Bill Frenzel (R-Minn.), has 299.

Chapoton argued before the subcommittee that the program is harmful because it not only drains the Treasury, but also increases the supply of tax-exempt bonds, driving up rates for all such borrowers.

He, Rivlin and representatives of GAO all termed the bonding mechanism an inefficient one for delivering subsidies.

"Only two-thirds of the benefits go to the beneficiaries," Chapoton said; the rest goes to high-income individuals who buy the bonds and financial institutions involved in issuing them. CAPTION: Picture, JOHN E. CHAPOTON . . . says program could cost $15 billion