Congress may have unintentionally given U.S. Capitol Police greatly expanded arrest authority for not only the District but also the rest of the country, House and Senate sources said yesterday.

The House-Senate conference report on the fiscal 1991 legislative branch appropriations bill, approved Saturday, the final day of the session, gave Capitol Police "additional authority to make arrests" anywhere in the District for a crime of violence committed in the Capitol, House or Senate office buildings or on Capitol Hill grounds.

In addition, the measure gave Capitol Police arrest authority for crimes of violence "committed in the presence of any member of the Capitol Police performing official duties" without limiting where the arrests could be made.

One interpretation of that provision, offered by a Capitol Hill official who asked not to be identified, was that it would give arrest authority to Capitol Police who are traveling in protective details for members of Congress.

That, however, was not the intent of the legislators who managed the $2.1 billion bill that funds operations of Congress and associated agencies, according to the House and Senate sources.

A spokesman for Sen. Harry M. Reid (D-Nev.), chairman of the Senate Appropriations legislative branch subcommittee and a manager of the bill, said Reid had intended to expand the Capitol Police arrest authority "on a step-by-step basis."

Reid, a former Capitol Police officer during his law school days, had originally proposed expanding the arrest authority to cover pursuit of criminals into the District after crimes were committed within the Capitol Hill complex. He also wanted to give Capitol Police authority to make arrests in the District when violent crimes were committed in the presence of on-duty Capitol Police officers.

When Rep. Vic Fazio (D-Calif.), chairman of the House Appropriations subcommittee on the legislative branch, introduced the conference report on the House floor Saturday, he offered no commentary. But he said, "An issue that divided the Senate and the House regarding the arrest powers of the Capitol Police who may have to pursue suspects into the District of Columbia has been compromised appropriately and given essentially to the authorizing committees to resolve."

Fazio was traveling in California yesterday, and an aide said his office is studying the language.

It appeared yesterday that only a handful of copies of the conference language were available on Capitol Hill. But one congressional aide familiar with the bill's drafting said, "The members were snookered."

Authority to make arrests anywhere in the country was originally sought by House Sergeant-at-Arms Jack Russ, who serves this year as chairman of the Capitol Police Board, governing body of the 1,340-officer force.

Russ said yesterday that the language approved by the conference is being studied by Capitol Police lawyers.

Dan Nichols, spokesman for Capitol Police Chief Frank A. Kerrigan, also said the legislative language was under study and that he was "not sure of the intent" of the congressional members involved.

The impact of the language may be short-lived, however. The conferees put a one-year limit on the new arrest authority provisions so that the House Administration Committee and the Senate Rules Committee could work out long-term arrangements.

Congress may amend the measure to eliminate any concerns when members return in January, a House aide noted.

Russ and the Capitol Police have been seeking the additional arrest authority since a D.C. Superior Court judge threw out a case in which Capitol Police officers arrested a suspected mugger off Capitol Hill based on information from witnesses.

Russ has also wanted the authority to make arrests in the District so his officers can intercede when they see crimes being committed as they travel between Capitol Hill and congressional facilities, such as the new offices in the Old Post Office Building.

Because of the increase in protective details for traveling members of Congress, Russ also wanted nationwide arrest authority should Capitol Police officers face any violence.

A House Appropriations subcommittee report last summer, however, questioned the need for an increase in such details.