The three-year contract between the region's four major grocery chains and the union representing some 15,000 supermarket employes expired this week, amid negotiations complicated by dramatically rising health care costs and a new method of bargaining, according to labor and management spokesmen.

The contract covering employes at Giant, Safeway, A & P, and Grand Union expired Sunday, but both sides agreed to continue talks, according to Thomas McNutt, president of Local 400 of the United Food and Commercial Workers.

Under the expired contract, experienced union supermarket employes earn between $11.23 and $13 hourly and are not required to contribute toward health and welfare fringe benefits that are managed by a joint labor-management plan.

But because of skyrocketing health care costs, the companies are facing a 58 percent cost increase just to maintain benefits that were agreed to in 1980, according to a Safeway spokesman. "Those kind of numbers make this a big economic issue," he said.

McNutt said employers now pay about $200 a month per employe for health coverage, but have projected the cost will increase to $410.

For nearly two decades, supermarkets have negotiated jointly through a Food Employers Labor Relations Association that has included as many as seven chains. But as some went out of business or left the Washington area, only four major chains remained and the companies, since 1980, have abandoned the association.

Local 400 formerly negotiated jointly for both Baltimore and Washington, but now has split those divisions. "

The local supermarket industry last had a strike in 1974. McNutt said past union policy has been to refuse to bargain past contract expiration dates, but he said the current complications necessitated the extension.