A tentative settlement was reached last night in a 12-day-old bakers' strike that has sharply raised the costs of bread for shoppers in 250 Giant and Safeway supermarkets in the Washington area.

Local 118 of the Bakery, Confectionary & Tobacco Workers' Union is expected to meet at 1 p.m. today to vote on the proposed new agreement between the 475-member union and the two chains.

Details of the new contract could not be learned, but a Giant spokesman said he was optimistic about ratification.

If the new pact is accepted, Giant spokesman Barry Scher added, the chain expects the bakers to be back at work by late today or by Friday. He said Giant products would then be back on store shelves no later than Saturday.

The striking workers normally bake 40 percent of the bread and baked goods consumed in the Washington area.

Before the strike, both Safeway and Giant had sold three loaves of their house-brand bread for $1 -- or 34 cents a loaf. At one point in the strike, with those brands absent from the shelves, the lowest-priced bread available was priced at 87 cents a loaf.

Subsequently at least one of the chains -- Giant -- began selling family-size loaves for 43 cents each, still substantially more than the price of Giant's private label products.

The chains traditionally have sold house-brand bread at lower prices than national brands because of lower advertising costs, experts say. The low-priced breads, also have been used to lure customers to the stores.

Wages, pension benefits and the chains' proposal for a baker's assistant position have been the major issues in the dispute.

Giant's Heidi Bakery bakers were paid $8.93 an hour under the old contract. The chains have offered an 85-cent-an-hour increase, but according to the chains, the bakers have sought $1 an hour.