The Socialist government cut back France's nuclear power program today by 25 percent, suspending construction of five plants despite the opposition of Communist Party-backed trade unions and right-wing parties.

A Cabinet decision, which overrode Communist ministers' objections, will mean the cancellation of equipment orders worth hundreds of millions of dollars and elimination of thousands of jobs. The decision is linked to a legislative debate on energy due in October, when the Socialist majority is expected to press for even more cuts.

Today's announcement concerned five nuclear power stations where initial work already has begun. They are part of a program for 20 atomic plants initiated by the Gaullist government in 1973.

President Francois Mitterrand's Cabinet backed down on canceling another partially built plant near Paris, where angry trade union members belonging to the Communist Party have held a series of protests this week -- blocking holiday traffic on the main roads.

The Communist-led Central Labor Confederation made it clear after the announcement on the plants that it would continue to oppose government policy. The Cabinet, presided over by Mitterrand, approved the completion of some nearly finished plants that also would have been halted if the president's electoral program had been followed in full. During the campaign it was proposed that 14 of the 20 projects should be suspended until an official inquiry and possible referendum.

A referendum still seems to be in the air, as "national and local consultation" on nuclear energy will be part of the parliamentary debate, but is already beyond doubt that France will not produce the amount of nuclear energy in 1990 that was presented as imperative by former president Valery Giscard d'Estaing.

Nuclear power already provides about a fifth of French electricity needs and was to have provided at least half, so France could end its dependence on imported oil.

Although the current cutback was less severe than expected, it came under heavy criticism from supporters of nuclear power and from ecologists.