The Environmental Protection Agency yesterday ordered General Motors Corp. to recall about 135,000 Cadillacs suspected of violating air-pollution standards because of defective carburetors.

The agency also said it is urging GM to recall voluntarily another 90,000 Cadillacs from the same 1975 model year, also for carbon monoxide emissions. The total number of cars involved amounts to 85 per cent of the Cadillacs produced that year.

It was the first auto recall ordered by the EPA's new administrator, Douglas M. Costle, who said he intends "to pursue a vigorous enforcement effort toward assuring that the nation's automobiles are as clean as federal standards dicate."

The Cadillac recall order was based on a defective carburetor design that EPA said had caused excessive emission of carbon monoxide. All of the Cadillacs with the carburetor tested by EPA exceeded the legal standards for carbon monoxide, and the average emissions were nearly three times that permitted by federal law.

A Cadillac spokesman said a plan for modifying the 135,000 carburetors would be submitted soon to EPA. If the plan is approved, owners will be notified by mail to take their Cadillacs to local garages for modification at the company's expense. The spokesman said the proposed modification would not require installation of new parts and could be accomplished in about 20 minutes.

The vehicles ordered recalled are equipped with 500-cubic-inch-displacement engines and include the Sedan DeVille, Coupe de Ville, Eldarado, Calais, Brougham and Fleetwood.

Costle, in a letter to GM President E. M. Estes, said he is also concerned that another 90,000 1975 Cadillacs may also be emitting excessive amounts of carbon monoxide and said he is continuing an EPA investigation of those vehicles.

He told Estes he is encountering "strong protestations" by GM that no violations exist on those cars. "I encourage you at this time to consider including these vehicles in the recall campaign," he said.

At his first news conference since becoming EPA administrators, Coastle also disclosed the initial phase of a crackdown on toxic chemicals. Congress last year gave EPA authority under the Toxic Substances Control Act.

He said he has started "a serious examination" of 15 chemical substances suspected of causing injury to human health or the environment.

The chemical substances are polybrominated biphenyls, phosphates, cadmium, benzene, asbestos, trichloroethylene, acrylonitrile, tris, hexachlorobenzene, lead, mercury, benzidine, arsenic, polynuclear aromatic hydrocarbons and vinylidene chloride.

An EPA official said those had been targeted for initial study because they seemed, on the basis of preliminary tests, to be potentially the most hazardous. Some are suspected of causing cancer.

Polybrominated biphenyls (PBB) have receive attention lately since being found in a flame retardant that accidentally was mixed with cattle feed in Michigan. More than 30,000 contaminated cattle and more than a million chickens were destroyed, the effects on humans is being studied.

Benzidine, which is used in dyes for textile, leather, and paper products, has caused liver and bladder cancer in animals and exposed workers. Tris is a flame retardant used in children's sleepwear. It is being investigated as a possible carcinogen by the National Cancer Institute.

Under the new law, EPA examine each substance and, if necessary, propose regulations that could lead to a range of orders, from outright prohibition to better labeling.

Costle said regulations on two other chemical substances, polychlorinated biphenyls and chlorofluorocarbons, will be proposed in April.