The U.S. Secret Service is considering a proposal to close off Pennsylvania Avenue to automobile traffic from 15th to 17th streets to increase security for the president and create a "campus-like" atmosphere around the White House, government officials disclosed yesterday.

Treasury Secretary James A. Baker III, whose department includes the Secret Service, confirmed yesterday that the proposal is under discussion, and said a final decision probably would be made by the White House. Both Baker and Secret Service officials said the concept was in the early stages of discussion.

The Secret Service has become more concerned about White House security lately as a result of terrorist activities overseas and a bombing at the U.S. Capitol in November 1983.

Federal and District officials said the proposal could be implemented easily, and may require only consent by the city's Public Works Department. City officials said they didn't know enough about the idea to comment on its impact, but City Council Chairman David A. Clarke said that closing off part of Pennsylvania Avenue "is going to create a traffic mess that's unfathomable.

"The street belongs to the people of the United States, not the president of the United States," Clarke said, adding that the Secret Service is "making a palace out of the place."

An aide to Mayor Marion Barry said the city would have to cooperate if the administration carries out the proposal.

A Treasury Department source said the idea arose a year ago as part of a long-range study of how to beef up White House security. Last year, East Executive Avenue was closed to traffic between the White House and the Treasury for security reasons.

The idea of closing Pennsylvania Avenue was disclosed at a hearing before a House Appropriations subcommittee on the Treasury Department budget, when Rep. Frank Wolf (R-Va.) asked Baker about it.

Baker declined to elaborate on the matter after the hearing, but Wolf said later that the Secret Service is "concerned about car bombs, truck bombs" crashing into the White House.

Wolf said that one idea is to put concrete barriers at 15th and 17th streets to keep out cars, while pedestrians would still be able to enter the area, which Wolf said would have a "campus-like" atmosphere. It was uncertain whether two streets flanking Lafayette Square, Jackson and Madison places, would also have to be closed because they intersect with the avenue.

Wolf said that Secret Service Director John Simpson told the subcommittee about the proposal last week, saying that any decision was several years away. Simpson promised to consult the subcommittee -- for Treasury, Postal Service and General Government -- before implementing the proposal, Wolf said.

A Secret Service spokesman said that what Simpson told the subcommittee "was merely a proposal, not a substantive plan," part of a continuing study to upgrade security around the White House. The spokesman also said that no firm decisions had been made about the proposal, including the questions of how much of Pennsylvania Avenue might be closed off, and how.

The spokesman said, however, that if the street were shut off it would be "strictly in the White House vicinity."

Wolf said such a plan would create chaos in downtown Washington, leading to traffic backups on bridges to Virginia and throughout Northern Virginia, where his district lies. According to the District's Department of Public Works, traffic on Pennsylvania Avenue between 15th and 17th streets averages 31,600 vehicles a day.

City public works officials said it was unclear whether that section of Pennsylvania Avenue was federal land or city-owned public right-of-way. Streets that were part of the original L'Enfant plan are owned by the federal government, but those two blocks of Pennsylvania Avenue don't appear as a street on the L'Enfant plan, so it is unclear where title lies.

"On the 1803 map, the section in front of the White House, including Lafayette Square and that section of Pennsylvania, appears as one big massive White House area," said Ralph Schafer, surveyor for the city.

Closings of city-owned streets must be approved by the D.C. City Council, but federal and city officials said that the Secret Service's proposal for Pennsylvania Avenue could be worked out between the Secret Service and the city public works office if it did not include transferring title of the land to some other entity. If the land is held by the federal government, the City Council would not have any say in the matter.

The Secret Service and the city public works department recently struck such a deal on the closing of East Executive Drive -- the street between the White House and the Treasury Building -- to vehicular traffic. Because it was left open to pedestrian traffic, the title of the land did not change hands and the proposal did not go before the City Council.