General Motors Corp. yesterday announced a new round of sales incentives designed to clear a bulging inventory of 1.2 million 1986-model cars and trucks from dealers' lots.

The GM sales incentives were announced as the backlog of unsold autos at the end of March reached its highest level in more than 20 years, as measured by Ward's Automotive Reports, an industry publication. Ward's said that the auto makers' stock was equivalent to a 76-day supply compared with 53 days a year ago.

The number of unsold cars among the nation's domestic auto makers as of April 1 reached more than 1.9 million units, the highest level since 1979 -- the year auto sales collapsed -- Automotive News reported yesterday.

The GM incentives include cut-rate financing programs ranging from 6.9 to 9.9 percent, depending on the vehicle purchased and the length of the loan financed by General Motors Acceptance Corp.

The low-interest financing -- compared with the 11 to 12 percent rates prevailing in the industry -- will offset a 2.9 percent price increase that auto industry analysts estimate will add an average $375 to the sticker prices of the company's new vehicles.

Those seemingly contradictory moves, which have brought criticism from GM dealers and workers alike, are part of GM's plan to get rid of its current glut of vehicles at a profit, according to some analysts.

GM's plan is to raise its base prices and then to discount from the higher base in hopes of making its sales-incentive programs more attractive, the analysts said.

Some 17 GM models are affected by the company's price hikes, including 12 that are in oversupply.

In all, GM had an 85-day supply as of April 1 compared with 78 days the month before and 51 days last year. Ford Motor Co. posted a 57-day supply, compared with 58 days last month and 56 days last year, Automotive News said.

Chrysler Corp.'s supply was an average 89 days vs. 90 days last month and 56 days a year ago. American Motors Corp. posted an average 142-day supply compared with 117 days last month and 109 days last year.

Ward's estimates were similar.

GM's overall dump-at-a-profit strategy might work because of the cover provided by huge price increases in Japanese cars, the analysts said.

Japanese auto makers have added an average 10.7 percent, or $1,028, to the price of their 1986-model cars since last January, analysts said.