Chrysler Corp. is increasing prices for its 1982-model year and extending its customer rebate program.

And General Motors Corp. said it is extending its program of reduced interest rates on new-car loans through Sept. 23 at the request of many of its dealers.

The Chrysler price increase will be an average 7.7 percent, or about $622 a car, for the start of the 1982 model year, the No. 3 automaker said today.

Chrysler's price increases are tentative, however, and could be reduced somewhat, depending on prices set by other automakers and on consumer reaction, said Harold K. Sperlich, president of Chrysler's North American Automotive Operations.

Sperlich said the increases, which were announced to Chrysler dealers by telegram, will remain tentative until the company's new models are introduced early in October.

GM already has announced tentative price increases averaging 6 percent, or about $617 a car, for its 1982 models. Ford Motor Co. hasn't announced prices for the 1982 model year.

Chrysler's increases were necessary to offset inflation and the fact that the No. 3 automaker had not raised its prices as much as its competitors during the 1981 model year, Sperlich said.

"You offset as much of inflation as you can with greater productivity," Sperlich said. "The rest simply has to be passed on.

"If you're looking for price reductions, the place where this country can get it and get it quickly is in interest rates," he added.

Few details were available, but Chrysler apparently concentrated the price increases in its best-selling cars in an attempt to squeeze the maximum amount of profit out of its sales.

The price of its lowest-priced Omni-Horizon Miser subcompacts will increase 8.7 percent to $5,976, while the bottom-line price for a K-car compact will go up 8.4 percent to $6,500.

Chrysler said part of the increase covers higher levels of standard equipment, along with increases in some option prices and higher delivery charges.

GM, the industry's pricing leader, said earlier that the 1982 model year may mark a change in its normal pattern of ordering relatively small price increases every three months or so.

GM said it wants to avoid such quarterly price hikes in the future. Its stiff tentative price increase also was seen as a tactic to encourage sales of leftover 1981 models, which currently are in oversupply.

GM launched its program of reduced-rate loans on July 28 to provide loans at 13.8 percent interest to customers at participating dealers. The offer was to have expired today.

The new ending date for the offer is one day before the introduction of several of GM's new 1982 car and truck models.

GM and the other major automakers began offering rebates and other incentives in late July and early August in an attempt to boost sales, which had fallen sharply since early June.

Chrysler has been offering rebates of between $300 and $1,000 on certain models; Ford has a dealer incentive program in effect that could mean customer savings of up to $1,000 a car; and American Motors Corp. also has been offering dealer incentives of between $100 and $450 a car.

Chrysler began offering rebates of $300 to $1,000 per car on Aug. 3. The offer had been scheduled to expire Monday.