Roman Catholic bishops have expressed mounting concern that legislation pending in Congress to provide medical benefits for pregnant employees would force employers to underwrite abortions for some employes.

The controversy has erupted over the pregnancy Disability Benefits Act. Which has been approved by House Education and Labor Subcomittee on Employment Opportunities. A proposed amendment to the bill, which would exempt mandatory payments for an abortion except in cases in which the life of the mother is threatened, was rejected by the sub-committee.

Bishop Thomas C. Kelly, general secretary of the U.S. Catholic Conference, issued a statement urging concerned persons to pressure Congress for the amendment to be restored.

Bishop Kelly, who praised the intent of the Pregancy Disability Benefits Act, said the amendment was necessary so that the law does not "coerce employers" who have religious or moral objections to abortion, into paying for the procedure.

If the law is adopted without such an amendment, he said, "Catholic dioceses, schools, hospitals and other insitutions of the Catholic Church would be forced by government to underwrite abortion benefits," he said.

In reporting on the issue to the administrative committee of the bishops, meeting here this week, Terence Cardinal Cooke, of New York, pointed out that passage of the unamended legislation would "create serious First Amendment problems in that it would penalize those whose religious beliefs conflict with a statutory mandate."

he warned that failure to comply with the proposed legislation could bring charges of violating the Civil Rights Act and could result in cancelation of government contracts - a severe disability for insitutions such as hospitals.

Cardinal Cooke also warned that "the present language of the bill would place the employer in a position where he could not lawfully accomodate his employes if they object to such coverage."

The New York churchman said the amendment, proposed by Rep. Edward Beard (D-R.I.), and which will be offered again when the full Education and Labor Committee considers the bill, would not prevent an employer from offering abortion as a health benefit.