The chairman of one of the leading Senate committees on the District has asked city officials to drop plans to close the firehouse that now responds to emergencies at the U.S. Capitol and the Supreme Court.

The city, in its newest budget has proposed closing down the firehouse, five blocks north of the Capitol at 439 New Jersey Ave. NW, and moving Engine Company No. 3 now housed there to a new facility being built on the other side of the Anacostia River at First and Atlantic streets SE, more than five miles away.

Sen. Charles McC. Mathias Jr. (R-Md.), chairman of the Senate Governmental Affairs subcommittee on the District, wrote Mayor Marion Barry on Feb. 19 urging him to keep the firehouse "manned and operating." The letter was cowritten by Sen. Thomas F. Eagleton (D -- Mo.), who is the committee's ranking minority member.

Sen. John Heinz (R-Pa.) and Rep. Stan Parris (R-Va.) have written separate letters to Barry asking that he reconsider the relocation proposal.

Mathias acted after receiving a letter from the Senate sergeant at arms, Larry E. Smith, also protesting the proposed move. "At a time of increased terrorist activity, I believe this is not the time to reduce the level of fire protection afforded the Nation's Capitol," Smith wrote.

Engine Co. 3, located directly across from the Hyatt Regency Hotel on Capitol Hill, is "first due" at the U.S. Capitol, the Senate office buildings, the Supreme Court, the Library of Congress, Union Station, and the shelter for homeless persons at 425 Second St. NW, in addition to numerous other nearby federal office buildings.

The company, which consists of a pumper and hose wagon, was first on the scene when terrorists exploded a bomb outside the Senate Chamber in November 1983. The station also houses an ambulance unit that is "of particular importance" to "the safety of Capitol Hill personnel," according to the Mathias-Eagleton letter.

Fire officials said they want to move the engine company to Ward 8, the city's poorest ward and most in need of additional fire protection. Currently only one firehouse serves most of the southern half of the ward.

However, according to Ken Cox, vice president of the International Association of Fire Fighters, Local 36, "We recommend an additional engine company" for that area of the city instead of relocating Engine 3. "This is like robbing Peter to pay Paul."

The budget does not indicate when the move would occur. A spokesman for the fire department could not be reached for comment on the proposed move.

Pauline A. Schneider, director of the D.C. Office of Intergovernmental Relations, said, "I understand it [the relocation] is being studied . . . . I was told no [final] decision has been made."