American Motors Corp. is phasing out production of its CJ Jeeps -- a modern-day version of the old World War II Army jeeps.

The Jeep CJ has been criticized as unsafe by consumer advocates and has been the subject of product-liability lawsuits, but company spokesman Jerry Sloan said the changing demands of customers, not concerns over its safety, prompted the Jeep model's demise.

The company said yesterday it will stop producing the CJ models in January and will replace it with a more comfortable all-new Jeep model that responds to "changing market conditions."

The Jeep CJ has been in production for more than 40 years, a direct descendant of the famed khaki-colored Army vehicle originally designed by the Willys Corp. in 1940. AMC purchased the Jeep operations from Kaiser in 1970 for $70.2 million. For years, the vehicle was a mainstay of the company's light truck fleet, which now also includes the Jeep Cherokee, Pioneer, Comanche and Grand Wagoneer light trucks and pickups.

More than 1.5 million civilian Jeeps have been built since 1945.

During the late 1970s and early 1980s, the CJ became the center of controversy over alleged safety defects that caused it to sometimes go out of control and overturn on sharp turns. The Federal Trade Commission ordered that an advisory sticker be placed on Jeep CJs in 1982, and, in a 1983 corporate prospectus, AMC reported that it was facing lawsuits totaling $2.5 billion in damages stemming from crashes related to the vehicles. AMC declined yesterday to provide any current figures, but a compilation by the Center for Auto Safety, a Washington-based research and advocacy group founded by Ralph Nader, said a total of 578 lawsuits have been filed over the CJ to date.

"It's a fine thing to stop producing this vehicle that has been such a consumer hazard, but what about all the hundreds of thousands of them still on the road?" said Clarence Ditlow, director of the center. "We feel that it is still unsafe . . . and the Reagan administration should have recalled them instead of letting them off the hook with a warning sticker."

Asked about the safety criticisms, Sloan replied: "We've contended that, if driven properly, the CJ would be completely safe. . . . The vehicle is not being phased out of production because of legal problems, I can assure you of that."

What did bump off the Jeep CJ, according to Sloan, is an evolving consumer demand to use such Army-type vehicles for standard "on road" use as well as rough "off road" driving.

"This is really to meet the demands of the Yuppies," said Sloan. "In the old days, people used to like to drive it mainly for off-roading -- over rocks, creeks, up steep hills, and down valleys. But now a lot of people are driving this type of vehicle to the bank in the morning in their pin-stripped suits. . . . So they want a more comfortable vehicle to drive when they have an attache case in the front seat and their Burberry coats folded in the back seat."

The trend toward more comfortable vehicles was reflected in a steady drop in demand for the old CJ. From a high of 79,296 units sold in 1978, sales of CJ models dropped to just 39,547 last year. Only 30,623 were sold during the first 10 months of 1985.

AMC has not released any details for its new Jeep model but said it will be built at its existing plant in Brampton, Ontario, starting in the spring of 1986. The company said there will be an undetermined number of layoffs among the 740 employes who work on the CJ at its Toledo, Ohio, Jeep plant, where the company also manufactures its other light trucks and pickups.