Protesters blocked the eastbound lanes of the Theodore Roosevelt Memorial Bridge yesterday morning, shutting down the bridge and clogging major routes into the District for thousands of Northern Virginia commuters for several hours.

The protesters -- members of the Justice for Janitors campaign who said they were demonstrating against proposed cuts in the District budget -- caused traffic backups for several miles on roadways west of the District, authorities said.

Virginia State Police spokeswoman Lucy Caldwell said the George Washington Memorial Parkway, Interstate 66 and Routes 50 and 110 "were basically a parking lot. . . . The residual effects lasted until about 11 a.m. -- it just brought traffic to a standstill."

Traffic on the four bridges that carry 137,000 commuters daily from Virginia to the District -- the Memorial, 14th Street, Key and Roosevelt -- was either stopped or moving only a few feet an hour, said John Undeland, a spokesman for the local American Automobile Association.

"It's safe to say that more than 100,000 people had their commutes disrupted by the stunt," Undeland said. "It's transportation terrorism, pure and simple. We are really concerned about this. We have seen more than a dozen of these incidents in the past year."

Yesterday's event began at 8 a.m., when members of the Service Employees International Union's Justice for Janitors campaign parked a large yellow school bus across the eastbound lanes of the bridge to protest D.C. budget cuts that affect children. Protesters set up a "classroom" in the middle lanes of the bridge, with desks, chairs and blackboards.

Dozens of exasperated passengers -- including Health and Human Services Secretary Donna E. Shalala -- abandoned car pools on the Roosevelt Bridge to walk into the District. Others lined up to make calls from the car telephones of frustrated fellow commuters.

"We feel that this little disruption is nothing compared with the major disruption the D.C. budget is going to have on working families and their kids," protester Deborah Dion said of the union, which represents 5,000 workers in the city.

Thirty-four of about 250 demonstrators were arrested, said Capt. Michael Radzilowski, of the D.C. police Special Operations Division. Radzilowski said such incidents are difficult -- if not impossible -- to prevent. "The problem is, you never know exactly what's going to happen."

Justice for Janitors has staged a campaign for higher pay for the workers who clean the city's office buildings at night and has focused much of its activity on real estate developer Oliver Carr.

The group has disrupted a D.C. Council meeting and blocked traffic before, including once on the 14th Street bridge during rush hour.

Yesterday's protest was cleared at 9:10 a.m. -- too late to spare the jangled nerves of commuters. John Wu, a computer specialist at the Department of Health and Human Services, said he briefly considered stopping Shalala as she walked past his car to a vehicle waiting on the D.C. side of the Roosevelt Bridge. "I was going to say, Excuse me, I'm going to be late,' " Wu said. But "she doesn't know me."

At least one driver blocked by the school bus feared the worst as it slowed down and turned sharply to obstruct several lanes of traffic.

"I thought, Oh, my God, let's not have some sort of terrorist activity here,' " said John Sly, a State Department employee whose car had been following the bus. "When they start blocking bridges off like this, people get really nervous." CAPTION: Rush-Hour Protest Police arrest Janitors for Justice protesters after the group used a school bus to block the eastbound lanes of the Theodore Roosevelt Memorial Bridge during morning rush hour. Demonstrators, who were protesting proposed cuts in the D.C. budget, also set up a "classroom" in the middle of the bridge. CAPTION: Commuters wait after demonstrators, protesting cuts in the D.C. budget, parked a school bus across the eastbound lanes of the Theodore Roosevelt Memorial Bridge during rush hour.