Chrysler Corp.'s new subcompact cars, the Dodge Omni and virtually scribed yesterday as "too risky to drive" by officials of Consumer's Union.

The auto manufacturer called the allegation, first reported in The Washington Post yesterday, "absolutely false."

Consumer's Union, an independent product-testing organization based in Mt. Vernon, N.Y., held simultaneous news conferences here and in New York to hand out advance copies of an evaluation of Omni and Horizon, scheduled for publication in the July issue of its magazine, Consumer Reports.

At the news conferences, a 43-second film showing stability tests of the two cars was used to illustrate what CU officials called "inferior emergency handling" by the cars. The alleged failure was blamed on "an inherent design problem."

Separately, General Motors Corp. announced yesterday the recall of some 598,000 passenger cars and pick-up trucks to correct fan blade and rear axle shaft problems.

Consumer's Union spokesman Mark Cymrot told reporters here that his organization has used tests applied to the Omni and Horizon on 150 other cars, including several with front-wheel drives, over several years. "We never had one with problems this serious," he added.

Omni and Horizon. which feature front-wheel drives, were introduced by Chrysler late last year in an attempt to increase the financially troubled firm's share of the U.S. auto market which had been declining.

The film showed what happened when a test driver took an Omni, which had power steering, up to 50 miles per hour, took his hands off the steering wheel and jiggled the steering wheel slightly. After seven seconds the car had veered off the road in almost a 180-degree circle.

"Other cars tested this way quickly return to their original course," said Cymrot. A similar test with a Horizon, without power steering, also resulted in swerving but not as dramatic as in the power-steering model.

The film also showed the same test being performed on a Datsun, which returned to its original course under its own power.

Still another brief part of the film showed an Omni as a test driver tried to take it through an obstacle course of yellow rubber cones. The car swerved, knocking over several cones before being brought under control by the driver.

Chrysler chassis engineering official Don Gschwind, who drove to the news conference in an Omni, stood outside CU's offices to deny that there is anything wrong with the cars. He said Chrysler officials said as much to CU when the firm was told of the test results "a couple of weeks ago."

"The test they used is meaningless," he said. "What consumer would subject a car to that? I can't imagine how a consumer would do something like that short of deliberately."

Gschwind said Chrysler had "not received one complaint" about the handling of the cars from consumers.

Although he called the CU experiment an "abusive test," Gschwind said Chrysler conducts a similar test in the early stages of development of its cars.

In the case of the Omni/Horizon, in Chrysler's own tests, the cars didn't experience the same degree of yaw," he said.

In a formal statement issued in Detroit, the nation's third-largest car maker said CU's demonstration "has no relationship to highway driving . . . It is grossly unfair to rate our cars on the basis of these abnormal demonstrations . . . Omni and Horizon owners and buyers may feel secure that there is nothing wrong with steering characteristics of these vehicles."

Chrysler's official in Washington, Gschwind also said, "we found at least one other vehicle with the same reaction (to the same test)," but he declined to identify the vehicle.

CU's Cymrot said the consumer group would not make any recommendation to consumers about selling the cars or about action they can take.

"We are not in a position to give advice," said CU Washington office chief Mark Silbergeld. "Consumers must take this information and then take their own action."

"We're recommending that consumers not to try to reenact this test," said Cymrot. "They should call the National Highway Traffic Safety Administration if they have any complaints."

Cymrot said NHTSA was alerted to the problem and shown the film earlier yesterday. He said CU had not received consumer complaints about the car until yesterday when "we received several calls," after The Washington Post's story outlining the problems.

The CU officials said they are giving the cars a "not acceptable" rating, the first such rating given to an American-made car in "at least a decade."

CU, as a regular service to the readers of Consumer Reports gives automobiles and many other products one of four ratings. "Not acceptable" is the lowest rating.

More than 165,000 Omnis and Horizons have been sold since they were introduced last January. The cars already account for nearly 20 percent of all Chrysler auto sales.

Meanwhile, General Motors announced the recall of nearly 830,000 of its 1978 Buick, Chevrolet, Oldsmobile and Pontiac full-sized, mid-sized and small passenger cars, and Chevrolet El Camino and GMC Cabellerro pick-ups equipped with certain V-6 and V-8engines.

GM said it is recalling the vehicles to check the engine fan blade because it could break under certain conditions, Dow Jones News Service reported.

GM said there have been no injuries reported. However, it suggested the engine on these vehicles shouldn't be run with the hood open until the fan has been inspected.

In addition, GM is recalling 265,000 mid-sized 1977 cars to determine whether the rear axle shafts require replacement. GM said the shaft on some of these vehicles may have a flaw in the metal which could result in shaft breakage and disengagement of a rear wheel.

The company said it has received reports of 15 minor injuries due to the defect. The models involved in the recall are Chevrolet Chevelle and Monte Carlo, Pontiac Lemans and Grand Prix, Buick Century and Oldsmobile Cutlass.