A federal judge said yesterday that the government's program requiring thousands of federal employes to pay for parking spaces at their jobs is illegal because President Carter did not submit the plan to Congress for approval.

In denying the government's request to throw out a suit brought by federal employes and six labor unions, U.S. District Judge Harold H. Greene said he would allow the government to make one more argument on other legal grounds in support of the year old plan.

The judge's opinion, which affects 75,000 federal workers in the Washington area and 350,000 throughout the country, made it clear that Greene considers the pay for parking plan illegal.

James R. Rosa, general counsel to the American Federation of Government Employes, said yesterday that Greene's finding was a "great step forward" in efforts by the federation and others who want the court to declare that the paid-parking regulations are unlawful and to require the government to return parking fees already paid.

Carter first announced that steps would be taken to eliminate free parking for federal employes in a nationwide speech on April 5, 1979, during which he stressed the severity of the nation's energy problem.

The end to free parking was one of several moves to cut down on energy consumption, Greene wrote in an 11-page opinion.

After Carter's speech, a circular published by the Office of Management and Budget established a policy for phasing in parking fees. The circular also gave the General Services Administration the authority to implement a plan.

Carter's decision to link the paid-parking plan to the government's energy-saving policy played a pivotal role in Greene's opinion.

Greene said it was clear that Carter, OMB and the GSA had not complied with the terms of the Energy Policy and Conservative Act, which says that restrictions intended to cut down on public or private energy consumption can become effective only after approved by Congress.

For example, Greene noted, restrictions on thermostat settings in government buildings were sent to Congress and approved there before taking effect. The paid-parking plan, however, "was never transmitted to Congress, and its implementation without congressional approval therefore is, on its face, a violation of the act."

Greene rejected the government's argument that it did not have to comply with the energy conservation statute because another law, the Federal Property and Administrative Service Act, gives the GSA administrator the authority to charge fees for parking spaces. The judge said that while that law gives GSA, the option of imposing fees for economic reasons, such as raising money to support government buildings, it does not allow plans to be implemented that are hinged to energy conservation.

"The law mandates that presidential energy conservation plans may become effective only upon scrutiny and approval by the Congress, and the court would not be justified in allowing the executive to avoid the accountability" to Congress that was envisioned in the energy conservation law, Greene wrote.

Greene said that the president may have been able to accomplish his parking fee objectives through an executive order -- if there was legitimate authority for such an order. However, Greene noted, no such order was ever issued in this case, so the question of Carter's authority to issue such an order was not before the court.

". . . The president made a public speech in which he announced his intention to impose certain energy conservation measures -- and that is all he did in regard to the subject under consideration in this case," Greene wrote.

"This is an insufficient basis for the exercise of lawful authority by the executive agencies," Greene said.

In the same opinion yesterday, Greene rejected the employes' argument that they had a constitutional right to have free parking spaces, which would require the government to hold a hearing before any parking fees were imposed.

Greene said that no law or collective bargaining agreement obligated the government to provide free parking spaces to federal workers.