SAN FRANCISCO (AP) _ The Teamsters union ended an 18-month strike Tuesday, signing a tentative, three-year contract agreement with the new owners of the Watsonville Canning and Frozen Food Co.

Terms of the agreement with Norcal Frozen Foods Inc. were not disclosed.

It is subject to ratification by members of Local 912. If the local ratifies the pact this week, the 1,000 strikers will begin going back to work Monday, the union said.

The strike, marked by sporadic violence, began in September 1985 after Watsonville Canning cut hourly wages by $6.66, reducing them to $5.15, and sought major contract concessions in health and welfare benefits.

Watsonville Canning signed over assets to creditors who now own Norcal on Friday, after Wells Fargo Bank began foreclosure proceedings because of $18 million in outstanding loans.

Norcal was formed by growers who were major creditors of Watsonville Canning. The growers were owed $7.3 million for produce that had been shipped on credit.

Watsonville Canning has frozen vegetables for growers including Birdseye and General Foods.

Norcal lawyer Dick Maltzman said the tentative agreement called for a wage level up to the ''industry standard.''