The House Appropriations Committee refused yesterday to renew a moratorium on oil drilling off California, reversing by one vote a position that has blocked exploration off much of the state for four years.

The 27-to-26 vote was a significant victory for the Reagan administration, which has sought for five years to increase drilling off California, and a setback for conservation groups, which have argued that the administration's ambitious plans do not adequately address environmental concerns.

The vote also is likely to scuttle efforts by some members of Congress from California to negotiate an end to the emotional stalemate.

The Californians reached tentative agreement with Interior Secretary Donald Hodel this summer that would have sharply limited drilling along the state's coast. The deal disintegrated two months ago, however, and the Californians had expressed hope that a renewed moratorium would entice Hodel back to the bargaining table.

"There's not much question that it's a serious blow to our efforts to find a balanced approach," said Rep. Leon E. Panetta (D-Calif.), who spearheaded the negotiations. "Our leverage was the moratorium."

In a statement, Hodel hailed the committee's action, saying the vote "enables America to proceed with an orderly and environmentally sound program" of energy development. The Interior Department's current plans call for a lease sale off southern California in late 1987.

But disappointed environmentalists said they would continue battling in the courts.

Oil drilling has been forbidden off much of California since 1981, when then-Interior Secretary James G. Watt's aggressive leasing policies turned the perennially sensitive subject into a politically explosive issue. Alarmed by Watt's far-reaching development plans, Californians succeeded in attaching the first moratorium to an appropriations bill. It has been renewed each year since, but support has been steadily eroding. Last year, the moratorium was renewed by a one-vote margin.

Yesterday, a letter from California Gov. George Deukmejian (R), strongly opposing the moratorium, tipped the scales the other way. In the past, Deukmejian's opposition had been muted.

The Appropriations panel action moves the battle to the House Interior and Insular Affairs Committee, where legislation is pending that would turn the summer's ill-fated agreement between Panetta's group and Hodel into law.

That measure, opposed by the oil industry and the administration, would permit drilling in 150 tracts, less than 3 percent of the area covered by the congressional bans, and put most of the coast off-limits to exploration until the end of the century.

In other action, the Appropriations panel approved, 24 to 16, a provision that would block an agreement between Interior and a group of California farmers seeking millions of dollars worth of subsidized federal water.

The Interior Department is reported close to announcing an agreement that would grant the water to the Westlands Water District near Fresno, reversing the government's longstanding legal position that Westlands farmers brought thousands of acres of land under irrigation illegally.

Under the provision approved yesterday, the department would need congressional authorization before signing the agreement.