Seven roads leading to the Capitol were blocked with trucks during the weekend as part of an experiment to tighten security, Capitol Police said yesterday.

The sudden appearance of roadblocks consisting of a ragtag collection of dump trucks and other trucks from Capitol grounds work crews, was not in response to a specific threat, they said.

"This is part of our ongoing program to tighten security," said Harry Grevey, deputy chief of the 1,225-member Capitol Police force.

Grevey said that officials will meet today to discuss whether to continue the roadblocks on a permanent basis during nonworking hours. The Capitol is more vulnerable to attack by a vehicle using one of the roads at those times, he said.

"We have additional personnel on duty during business hours and we have the flow of the traffic outbound along those driveways," he said. "So a car coming the wrong way during business hours would be picked up pretty quickly.

"But during nonbusiness hours, with no cars parked on the driveways and no outgoing traffic, it would be easy for a vehicle to reach the target."

To block vehicle access to those roads, officials parked the trucks at the end of these drives: Northeast, Maryland Avenue, Congressional, Southeast, South Capitol, Southwest and Northwest. In addition, there was a truck at each of the two entrances to the Capitol, where security guards are stationed to check vehicles entering the grounds.

East Capitol Street, the remaining driveway, was blocked to ingoing and outgoing traffic earlier this year by large concrete barriers that also serve as flower pots.

The concrete barriers were among steps taken to increase security at the Capitol after a bomb containing about three pounds of dynamite exploded in a corridor 30 feet from the Senate chamber last Nov. 7.

The bomb caused about $250,000 damage, but no one was injured. A terrorist group is a prime suspect in that bombing, according to FBI Special Agent Ron Dervish, but he declined to identify the group.

Besides erecting barriers to vehicular traffic at the Capitol, the White House and some other federal buildings, security officials have installed metal detectors at entrances to the Capitol and installed bullet-proof metal in the backs of chairs on the floor of the House of Representatives. And a strict employe pass program has been started.

One Senate aide said yesterday that the security campaign on Capitol Hill has intensified since the latest bombing of the American Embassy in Lebanon, on Sept. 20.

"They are just nervous, and with good cause," the aide said. "They have had threats all along, and that is why they have undertaken this. But the nature of the threats makes it difficult, because the threat will be something like 'A major institution in Washington will be hit.' "

A bomb blast caused minor damage to an office building at 600 Pennsylvania Ave. SE over during the weekend, D.C. police said.

Police said that they have no information on who planted the explosive device, which was left near the entrance to the American Civil Liberties Union office on the third floor of the building.

Police said that no one was injured in the explosion, which occurred at 9:55 a.m. on Saturday.