A joint venture operated by two of the world's largest auto makers, General Motors Corp. and Japan's Toyota Motor Corp., will start rolling a new subcompact car off its assembly lines on Dec. 4, GM officials said yesterday.

New United Motor Manufacturing Inc., the joint-venture company based in Fremont, Calif., will produce up to 250,000 Nova subcompacts annually for U.S. sales under GM's Chevrolet nameplate.

The joint-production agreement also gives Toyota the option to assemble some of its own cars at the Fremont plant for U.S. distribution.

The addition of the front-wheel-drive, 4-cylinder Nova to the Chevrolet lineup will give GM one of the biggest fleets of subcompacts in the U.S. auto market.

That point has prompted Chrysler Corp. to file an antitrust suit against GM and Toyota.

The petition, filed in federal court here last April, alleges that the venture constitutes "an illegal price-fixing agreement," inasmuch as GM and Toyota compete against each other in the same market in which their joint venture operates.

The two companies "will inevitably set the price of their own products in relation to their agreed-upon price for the joint-venture product," a summary of the Chrysler suit says.

"The anticompetitive consequences of this price-fixing will" affect larger cars as well, because auto companies "must consider the prices of cars in higher and lower segments of the market" in setting prices, the Chrysler suit says.

Chrysler Executive Vice President Bennett Bidwell, in an interview with United Press International in Detroit, said that his company will press the suit, even though the Nova will be three to four months into production by the time the case is heard.

"We don't intend to give up," Bidwell said.

GM officials yesterday declined comment.

But in court papers filed in conjunction with the Chrysler suit, GM said in part: "GM is confident that, when this case has run its course, Chrysler's lawsuit will be exposed as a sham. Despite its hypocritical declarations in this case, Chrysler . . . has not brought this action to protect competition in the automobile industry."

The term "hypocritical" refers to Chrysler's current annual importation of about 87,000 cars from its Japanese partner, Mitsubishi Motors Corp., for U.S. sales.

But analysts say that Chrysler's consternation -- as well as some misgivings by Ford Motor Co. and American Motors Corp. -- over the GM-Toyota deal is understandable.

With help from the Japanese, GM's small car lineup is becoming formidable -- and would grow to even greater strength if, and when, the so-called "voluntary" quotas limiting the shipment of Japanese cars to the U.S. are lifted. Those quotas have been in place since April 1981.

The Nova will join GM's best-selling J-body subcompacts, led by the 2-liter, 4-cylinder Chevrolet Cavalier.

Also in that lineup are the 1.5-liter, 4-cylinder Spectrum, made for Chevrolet by Isuzu Motors Ltd. and sold in 16 Eastern states; and the 1-liter, 3-cylinder Sprint minicar, made for Chevrolet by Suzuki Motor Co. Ltd., and sold in nine Western states.

The Spectrum and Sprint are high-quality, nimble, fuel-efficient commuter cars. GM had hoped to sell about 200,000 Spectrums and 84,000 Sprints for the 1985-model year, but is falling far short of those numbers because of limitations on Japanese imports.

The 10-year-old, rear-wheel-drive, 1.6-liter, 4-cylinder Chevrolet Chevette/Pontiac 1000 cars are also in GM's subcompact lineup. But many analysts believe that these cars, currently assembled by GM in Lakewood, Ga., do not have the right stuff to hold up in competition against the newer subcompacts.

Analysts say that the cars are too close in price.

For example, the Spectrum 2-door hatchback carries a manufacturer's suggested retail price price of $6,295 -- $995 more than the Chevette 2-door hatchback ($5,340) and $1,144 more than the Sprint ($5,151), according to latest new-car price surveys by Automotive News, an auto industry trade journal.

Even some GM officials admit privately that there is not enough price difference among their subcompacts to hold on to the Chevettes and Pontiac 1000s. But they deny that they are working a corporate squeeze play to get the older subcompacts out of the market.

"We're not trying to kill the Chevette," one of those officials said. "But it has been around since 1975.

"It's a good car, but we're going to let the market decide if it is good enough to stay around a little longer," the offical said.