D.C. officials said yesterday that they would explore all legal options, including suing the federal government, if the Secret Service or another federal agency moves to restrict traffic on 15th Street NW east of the White House and the Treasury building in response to a heightened security alert.

"We should be in court the next minute," said D.C. Council member Jack Evans (D-Ward 2), whose downtown district includes the area around the White House. "We can't always be in a reactionary mode."

A Secret Service spokeswoman, Lorie Lewis, said federal agencies are working with local officials -- and will continue to do so -- to decide what precautions are needed in the wake of the recent terror alert at the Treasury building and other major financial institutions.

The Secret Service announced earlier this week that it would close the west sidewalk on a two-block stretch of 15th Street to pedestrians within a few days, once it obtains the metal barricades to do so. Federal officials are discussing with local officials the possibility of barring trucks from that portion of the road -- a move that would be similar to one taken jointly two years ago by federal and D.C. officials on an eight-block stretch of 17th Street, west of the White House.

Mayor Anthony A. Williams (D) praised the collaboration this week, saying he much prefers that approach to the unilateral decision by U.S. Capitol Police Chief Terrance W. Gainer to shut down First Street east of the Capitol starting Tuesday morning.

But a spokesman for Williams also agreed with Evans that the city should be prepared to seek a restraining order or other court intervention if the Secret Service moves to close 15th Street to some or all motor vehicle traffic without city agreement.

"We should be ready, and we are getting ready," said Tony Bullock, the mayor's director of communications. "The mayor has said he would fight these closures with 'every fiber of his being.' I think a lawsuit would come under the general category of every fiber of your being."

D.C. Attorney General Robert J. Spagnoletti yesterday completed a report for Williams summarizing who has legal control of which streets and what the city's options are for challenging closures. City officials would not discuss those options in detail.

Williams and other local officials say that closing streets wreaks havoc on traffic and tourism and damages the city's sense of well-being without eliminating the threat of terror attacks. Less disruptive methods, such as increased police presence and checkpoints, would be sufficient responses to the heightened alerts, they say. They often cite the examples of Pennsylvania Avenue NW in front of the White House and E Street NW in back of it to illustrate the ill effects of downtown street closures.

A spokeswoman for Spagnoletti said the city has authority over all streets except for the Capitol complex -- an area roughly bounded on the west by Washington Avenue, Third Street NW, Constitution Avenue, Louisiana Avenue and North Capitol Street; on the north by D Street; on the east by Second Street, extending to Third Street between East Capitol Street and Independence Avenue; and to the south by the 100 block of C Street SE, as well as D Street between First Street SE and Washington Avenue.

Federal agencies control the sidewalks outside their buildings, however, and can prohibit parking outside buildings where federal law enforcement activities are taking place.

Because of the District's unique status as a city ultimately under the control of the federal government, Congress can vote to close any street without the D.C. government's approval, Spagnoletti spokeswoman Tarifah Coaxum said.

Terror alerts have federal officials weighing closing the street east of the Treasury building.