The nation's Big Three auto makers, in an effort to reduce bulging inventories of 1985 cars, have begun an interest-rate war that could give new-car buyers some of the best financing terms since the recession of 1983.

Chrysler Corp. is offering 7.5 percent financing on a wide range of cars and trucks, and General Motors Corp. and Ford Motor Co. have put a 7.7 percent yearly financing rate on many of their vehicles.

The cut-rate financing is being offered only on 1985 models in dealer stocks.

Dealer lots are swollen now by 600,000 cars that were manufactured during the auto-transport drivers strike that ended Monday.

The sales incentive campaigns involve price cuts made by manufacturers as well as contributions by new-car dealers who are participating in the programs.

The 7.5 percent to 7.7 percent corporate-sponsored financing rates are at least 3.5 percentage points below the lowest rates being offered on new car and truck loans by banks in the Washington metropolitan area.

A survey of area banks yesterday showed annual financing rates for 1985-model cars and trucks ranging from 11 percent to 13.7 percent for a 36-month or 48-month loan. Rates generally are higher for longer term loans.

Some local banks charge the same rates for 36-month and 48-month loans, but their rates tend to be higher than those at banks using the split-rate system.

The lowest rates at most banks are available only to customers who make a down payment of 20 percent or more of the price of the car, but the auto makers' discount rates apply regardless of down payment.

The recently ended strike by Teamsters union members who deliver cars to dealers worsened what was already turning into a troublesome oversupply of cars for the Big Three companies. Their sales are off largely because of increasing difficulty in selling mid-size and luxury cars.

"Their sales were down about 10 percent from a year ago some 40 days before the truckers' strike," said Arvid Jouppi, president of Arvid Jouppi Associates Inc., a Detroit-based firm that analyzes developments in basic industries. "The truckers' strike," by comparison, "was just an incident."

Jouppi said there is evidence that buyers with family incomes of $22,000 or more -- the people who led the domestic auto industry out of its recent recession -- are beginning to spend their money on things other than cars.

"It looks like that market and even the luxury car market is saturated," he said.

At the same time, there is heated competition between domestic and foreign car makers for buyers at the lower end of the auto market, Jouppi said.

"The market for buyers with family incomes under $22,000 is like a loose ball on the court. Everybody is going after it," including the Koreans and now the Yugoslavians, Jouppi said. That means a declining share of the U.S. small-car market for traditional U.S. auto makers, according to Jouppi.

GM, America's biggest car company, has seen its overall U.S. market share fall to 56.5 percent during the first six months of this year from 59.3 percent during the same period a year ago.

Ford increased its market share from 23.8 percent to 25.1 percent during the period, and Chrysler went up from 12.1 percent to 14 percent. Analysts believe that Ford and Chrysler gained at GM's expense.

GM began attempting to recapture part of the lost business in June with a 9.9 percent financing program on its front-wheel-drive luxury cars and 8.8 percent financing for its pickup trucks.

GM's new 7.7 percent plan covers 30 different models of cars and trucks.

"Anytime you can get money market loans at below 8 percent, when financial institutions are charging substantially more than that, it's a good deal," said J. Ferron, executive director of industry analysis and dealership operations at the National Automobile Dealers Association in McLean.

Ferron said participating dealers "are uncertain about the effects" of the below-8 percent campaigns. "If there isn't a response, then there may be a market out there that we don't know about," he said.

The dealers are under pressure to get rid of their inventories of 1985 models before the 1986 cars arrive in early October, Ferron said. "They have to do something to make room for those new cars," he said.

The Chrysler campaign ends Oct. 5. GM and Ford will end their programs Oct. 2