General Motor Corp. announced rebates of $500 to $700 on half its cars yesterday, prompting Ford Motor Co. to counter immediately with rebates of 10 percent of base prices for roughly the same proportion of its models.

Industry analysts said Chrysler Corp. would be forced to extend its 11-week-old program of 7 percent rebates of the total sticker price for all but one model.

A GM spokesman said the No. 1 automaker, always the most reluctant to cut prices and frequently critical of other manufacturs' rebates, had been forced into action by the competition.

GM's share of the market for domestic makes dropped from 62.4 percent in January to 57.8 percent for the first 10 days of February.

Chrysler's offer of a rebate equal to 7 percent of the sticker price largely accounts for the gain in its share of the auto market from about 9 percent late in November to 11.7 percent so far in 1981 and 11.2 percent in early February.

Chrysler spokesman Tom Jakobowski said, "We have nothing to add [about the offer] right now."

Asked if Chrysler would extend its offer or have some other countermove, an executive usually familiar with Chrysler's plans replied, "You'd better believe it."

American Motors Corp., anticipating GM's announcement, said Monday it would extend 10 percent price cuts past their sheduled ending Friday to March 15. GM's rebates will end March 19 and Ford's on March 21.

Here are current price cuts or rebates for the domestic auto manfacturers: GENERAL MOTORS CORP.

Chevrolet Chevett and the X-car family -- Chevrolet Citation, Pontiac Phoenix, Oldsmobile Omega and Buick Skylark.

Chevrolet Camaro and Monte Carlo, Pontiac Firebird and Grand Prix, Oldsmobile Cutlass Supreme and Buick Regal. FORD MOTOR CO.

1981 models: 10 percent of base vehicle price, excluding options, on the Ford Fairmont, Granada, Mustang and Thunderbird; Mercury Zephyr, Capri, Cougar and XR-7; and Lincoln and Lincoln Continental.

1980 models: $600 for the Ford Fairmont, Granada, Mustang and Thunderbird; $700 for the Mercury Zephyr, Cougar, Capri and XR-7; and $1,000 for the Lincoln and Lincoln Continental. CHRYSLER CORP.

7 percent of total sticker price, including options, on all imported and domestically produced cars, except the Imperial. AMERICAN MOTORS CORP.

10 percent of base sticker price on all cars, excluding options. Jeeps and Renault models are not included. VOLKSWAGEN OF AMERICA

No rebates or dicounts in effect.