Forty-three deputy U.S. marshals in Washington who expected to be without jobs on Jan. 29 may have won a two-month reprieve Friday when the Senate gave final approval to a bill to increase agency funding levels until March 31.

The deputy marshals -- more than a third of the work force in the District -- were told last month they would be included in a reduction in force mandated by Reagan administration budget cutbacks.

The money that now may be available to the U.S. Marshals Service is part of the Department of Justice appropriation. A Senate appropriations committee source warned yesterday, however, that so far there is no official guarantee that Justice would use those funds to delay the RIFs.

A Justice spokesman said last night that budget analysts say it may take until January to determine whether the money is available to delay the Marshals Service cutbacks. The spokesman said House and Senate conferees earlier decided that $5 million in Justice appropriations should go to the department's supervision of bankruptcies, which could reduce money available to avoid the marshal RIFs.

"The budget people say . . . it's going to take a while to sort it all out," the spokesman said.

Sen. Lowell P. Weicker (R-Conn.), chairman of the Senate subcommitte on appropriations that handles Justice, said on the Senate floor Thursday night that he expected the extra money would mean the marshal RIFs would be canceled.

Sources at D.C. Superior Court, which would be hardest hit by a cutback in marshal service, said, however, that the two-month extension only postpones an inevitable confrontation with federal officials about using marshals to staff local courts. Unlike any other district in the country, the District of Columbia uses marshals to provide security in the local courts, transport prisoners and execute court orders, such as warrants.