FBI Director William H. Webster voiced skepticism yesterday on a proposal to ban traffic in an area around the White House for security reasons, saying the idea might backfire.

"Sometimes excessive security actually invites trouble," Webster said in an interview with wire services. He said he is concerned that elaborate security measures would be a victory for terrorists by leaving the impression that the U.S. had been forced into "a siege mentality."

The U.S. Secret Service is considering a proposal to close off Pennsylvania Avenue to vehicles between 15th and 17th streets NW to increase security for the president. Under the proposal, a "campus-like" atmosphere would be created and pedestrians could still enter the area.

A Secret Service spokesman said yesterday that closing off the blocks to traffic is "no more than an idea . . . We have not presented a concrete plan to Treasury."

If the Secret Service makes a recommendation, it would have to be considered by the Treasury Department and the White House and probably Congress, a spokesman said.

The District would have to be consulted, but spokespersons for the Secret Service, Treasury and the D.C. Department of Public Works said yesterday that it is not clear whether the city would have to approve such a plan before it could go into effect. None of them could say which government entity owns and controls the street.

East Executive Avenue, the eastern border of the White House compound, was closed to traffic in 1983. In addition, concrete barriers were placed in front of the White House as an increased security measure, and Webster yesterday called that precaution "quite prudent."

But excessive security would give a terrorist "a sense of having achieved success without having to run any risks," Webster said in the interview, according to the Associated Press.

"If he can have a great country going into siege mentality, it is a form of victory for terrorist groups, and we shouldn't do that," he said.

Webster said security measures should be as inconspicuous as possible and that the U.S. is dealing rationally with potential security threats. "Of course, we went through a period of vaporous intelligence about different kinds of hit teams coming to the United States. That continues. But I don't think it has the city in its grip at all."