The savings and loan industry, the main source of funds for home mortgages in the United States, is waging a vigorous campaign to fend off a proposal by the Carter administration to reduce savings and loan associations' allowable reserve for bad debts.

Although the prospect of Congress enacting much of the President's tax package seems dimmer with each passing day, the thrift industry is not taking anything for granted.

"It looks like it is going to right down to the wire," said Philip Gasteyer, associate Washington office director and staff vice president of the United States League of Savings Associations.

The House Ways and Means Committee began making tentative decisions on the tax package during the week of April 17th. Not many of the administration's proposals were accepted.

In testimony before the committee, Junius Baxter of Denver, vice chairman of the U.S. League's legislative committee, told the committee the administration's proposals would reduce the amount of S&L money available for housing by $61 billion - enough to finance 1.2 million homes - by 1990.

The Treasury Department, said Baxter, "indicates a serious lack of understanding" about the role the bad debt reserves play in enabling S&Ls to operate.

The Treasury, however, stuck to its guns and said the reduction of the bad debt reserve is a necessary step toward tax equality among financial institutions. The administration also proposes to eliminate the bad debt reserve for commercial banks in 1979 instead of 1987, as provided in present law. Instead, commercial banks would establish reserves for losses based on experience, just as other business do.

The administration also proposes to phase in a tax credit unions. By 1982, under the administration approach, credit unions would be taxed the same as savings and loan associations and mutual saving banks.