And libraries that used to search patrons on the way out, to prevent book theft, are now searching them on the way in _ to prevent the unthinkable.

"This is the new normal," Al O'Leary, spokesman for the city's transit authority, said of the shutdown of several subway trains during the morning rush Monday.

This time, it was a suspicious package and two "suspicious powder incidents," O'Leary said. But before the all-clear was given, commuters forced off the subway at 34th Street and Sixth Avenue demanded to know when service would be restored.

"Could be five minutes, could be the whole day," an exasperated cop posted outside the station said. "Where you been? Don't you know what's going on in this town?"

Such is life in New York City, post-Sept. 11. Delays on public transportation are the norm; people who have worked in the same building for years must show ID and have their bags searched every time they come in.

"That's the routine now," said Cecilia Paryag, one of tens of thousands of commuters inconvenienced by Monday's train troubles. "We're going through this every day."

Authorities warn that hoaxers will be dealt with severely. Stephen Evers, 39, of Newburgh, N.Y., was charged last week with threatening to use a weapon of mass destruction _ a charge that carries a potential life sentence _ after he allegedly poured baby powder into a supermarket worker's pay envelope as a hoax.

But most of the recent scares appear innocent. In Grand Central Terminal on Friday, an area where white dust was spotted was cordoned off and the substance was sent for testing.

"Somebody had apparently dropped a powdered doughnut," said Margie Anders, a spokeswoman for Metro-North Commuter Rail Road, which runs trains from Grand Central to the suburbs.

New Yorkers lucky enough to get tickets to the post-season Yankees games can no longer come straight from work with briefcases and knapsacks. Bags have been banned from Yankee Stadium.

"The briefcase absentmindedly left behind on the subway platform would have been sent to the lost-and-found before this," O'Leary said. Now, he said, the police are called in and the briefcase is X-rayed.

The Brooklyn company that makes the sugar substitute Sweet'N Low has stopped offering free samples from its Web site.

"We were getting calls from the FBI and the police from people who got the packets in the mail," said Marvin Eisenstadt, who runs the family-owned business. "They had forgotten that they ordered it," and feared anthrax.

A guard now stands outside the mixing room at the Sweet'N Low factory. "And we're being very careful that we don't have any leaky packets," Eisenstadt said. "People see white powder, they get paranoid."

City traffic patterns change daily as police and soldiers in fatigues establish rotating checkpoints to pull over vans and trucks.

Two weekends ago, a man was spotted at a ferry terminal leaving a knapsack next to a garbage can. Someone called the police, and the area was evacuated until the bomb squad determined that it was ... a discarded knapsack.

"It's a pain in the neck," said Winsome Wallace, who was trying in vain to get a train to the Bronx from Manhattan during Monday's delays. "But I'm glad they're taking precautions."