NORFOLK, FEB. 5 -- At least a dozen bomb scares tied up morning rush-hour traffic and heightened anxiety in this military center today, a day after six pipe bombs were found attached to a pair of giant chemical storage tanks.

Police and fire officials throughout the Hampton Roads area spent much of the day fielding anonymous bomb threats, evacuating buildings, closing roads and searching for explosives. No bombs were found, and authorities attributed the flurry of threats to pranksters.

"It's just sparked people to go crazy," said Officer Karl Morrisette of the Portsmouth Police Department.

At the same time, law enforcement officials reported no leads or suspects in their investigation of the six pipe bombs, which were successfully removed from two tanks in the Berkley section of Norfolk on Monday. They stressed that no evidence has been found either linking them to the Persian Gulf War or ruling out such a link.

"I can't say it's going to {turn out to} be terrorism, not in any good conscience," said FBI Special Agent Jim Watters.

Experts said the incident did not fit the typical pattern of terrorists' work. Usually, a group immediately claims responsibility so that its cause gets media attention; no group claimed to have planted the Norfolk bombs. Also, experts said it is unlikely that a terrorist would have planted such pipe bombs.

However, the bombs and the subsequent threats did accomplish a terrorist goal of stirring fear.

"I am highly nervous about this," said Virginia Richardson, of Norfolk, whose balloon business has outlets on several military installations and malls. "I feel like we're sitting on a powder keg and that anything can go off at any time."

Home of the world's largest naval base and nearly a dozen other military installations, Hampton Roads has dispatched about 40,000 service members to the Persian Gulf War.

Elsewhere in the region today, a crude homemade bomb damaged a bathroom in the student center at Frostburg (Md.) State University, the State Fire Marshal's Office said. No one was injured, and investigators do not believe the bomb was set by terrorists.

Today's bomb threats in the Hampton Roads area were scattered at both civilian and military sites and did not appear to fit any pattern, suggesting to police that they were the work of attention-seekers rather than organized terrorists.

"In any kind of situation like this, you have copycat activity," said Jess Zimmerman, of the Center for Strategic and International Studies in Washington.

The most serious scare today closed the Downtown Tunnel linking Portsmouth and Norfolk for almost four hours beginning just after 8 a.m., clogging alternate routes for hundreds of drivers until authorities reopened the tunnel after finding no bomb inside.

The tunnel was closed again for almost an hour tonight, starting at 7:55 p.m., after a suspicious-looking bag was found. The bag turned out to be empty.

The tunnel, the second-busiest of the area's four tunnels, carries Interstate 264 under the Elizabeth River between Portsmouth and Norfolk. About 80,000 vehicles use it each day.

A man called the Virginia Department of Transportation's tunnel office at 8:08 a.m. saying two bombs were in the tunnel.

Searching the tunnel was difficult and time-consuming, officials said, because there are air vents above and below the roadway that remove exhaust and replace it with fresh air. However, Virginia State Police squads found no bomb in any of the areas, and the tunnel was reopened at 11:50 a.m.

In addition to the bomb threats at local schools, colleges, businesses and two malls, an enlisted man at the Navy's Dam Neck Fleet Combat Training Center in Virginia Beach noticed two suspicious packages between two barracks this morning. They turned out to be a pipe and a shoebox, according to Navy officials. A Navy bomb squad blew up the shoebox, which was empty.

At Newport News Shipbuilding, one of the nation's largest shipyards, a caller threatened to place a bomb near the docks where the company is building 13 ships for the U.S. Navy and repairing the USS Enterprise aircraft carrier. No bomb was found, a company official said.

In ways large and small, local residents have been making changes that reflect their concern since the war began last month.

Military police and local shipyard security guards have been more rigorous in checking identification in buildings as well as at gates, and in conducting random searches of cars. Transportation officials discussed installing caller-identification telephone service after today's tunnel threat.

Local businesses fretted that the nationwide publicity could hurt travel and tourism. The manager of the Omni International Hotel in downtown Norfolk said several out-of-towners with reservations called today asking about the pipe bombs.

Stella Fronzaglio, a waitress from Virginia Beach, said she would not take the Downtown Tunnel home from work for several days "for fear there's a bomb there. That's being silly, but I'm superstitious."

Mary Ann Tetreault, a terrorism expert at Old Dominion University, said that regardless of whether the bombs were the work of terrorists, "it scared local people."

"You don't really need a hole in the ground to frighten people," she said. "In a way, it's almost worse and more frightening when nothing happens because you imagine the worst."Staff writer John Ward Anderson contributed to this report.