NEW YORK (AP) _ A union representing 40,000 General Electric Co. workers has ratified a new three-year contract and 11 smaller unions are expected to follow suit, labor leaders said today.

The vote was almost 5-to-1 in favor of the pact, said Jerry Borstel, a spokesman for the International Union of Electronic Workers.

All but two of the 72 locals had reported, Borstel said, with 66 approving the contract, three rejecting it and one split evenly. The two locals who had not reported represent 20 workers.

The vote count was 33,378 in favor and 6,785 against.

''The overwhelming vote to ratify shows that the IUE membership is satisfied with this settlement, which is worth more than the 1985 contract and is better than any other agreement negotiated in the industry this year,'' said IUE President William Bywater.

The IUE is the company's largest union.

Bywater said he expected the 11 smaller unions that joined the IUE at the bargaining table to ratify the contract, including the United Electrical, Radio and Machine Workers of America.

United Electrical has called the contract inadequate, but said in a statement last week: ''We cannot lead our members into a long strike that has virtually no chance of success because of the lack of unity within the IUE.''

The UE leadership recommended that its 25 locals accept a pact when they vote Friday that is virtually identical to the IUE offer.

Two days after the tentative agreement was reached June 26, a group of IUE delegates from locals nationwide who were not party to the negotiations recommended that members reject it. Bywater traveled around the country urging support.

The contract calls for a special early retirement package; three annual wage increases of 2.5 percent, 1.5 percent and 1.5 percent; two cash bonuses; reduced employee pension contributions; preferential hiring for IUE members; dependent care aid, and other improvements.

The average hourly wage of $12.02 would rise to $13.40, assuming 4.5 percent annual inflation, according to GE figures. The average employee stands to gain about $6,100 over the life of the contract.

Workers covered by the pact produce everything from light bulbs to appliances, medical equipment to aerospace products, and maintain factories and machinery.

GE's offer must be ratified by all its unions by Sunday for its terms to be retroactive, GE spokesman Jack Batty said.