Millions of Americans crowded streets and malls for millennial celebrations last night even as FBI agents and their Canadian counterparts remained on a heightened state of alert because of an alleged Algerian terrorist plot to disrupt the festivities.

The worst fears about the New Year being accompanied by high-profile violence faded as midnight celebrations went off without incident on the East Coast, but only after authorities had swept up dozens of people for questioning.

Law enforcement officials stepped up their efforts as festivities approached, seeking more leads yesterday about possible terrorists. Their inquiries followed by one day the arrest and detention of a number of Algerians in New York and Boston who generally have not been cooperating with authorities, leaving unanswered the question of whether other militants may be active in the country.

FBI spokesman John Collingwood said the questioning of people who may know something about the plot was proceeding yesterday on an "expedited basis and on an international basis to ensure that no piece of information remains unexplored."

FBI agents focused yesterday on people who may have information about either the Armed Islamic Group, an Algerian terrorist organization that has never targeted the United States before, or Ahmed Ressam, the man caught carrying explosives from Canada into Washington state on Dec. 14. He allegedly was at the center of the group's plan to carry out attacks that authorities believe were aimed at millennial celebrations.

While federal law enforcement officials have not identified any specific U.S. city or site that could be the focus of an attack, they remain concerned that others with links to the Algerian terrorist group may have eluded their nationwide manhunt.

"We are obviously all over the country today, set up in every field office, following up on every piece of information that comes to our attention from every source," Collingwood said. "We are talking with people whose name surfaced during the course of the investigation and may be in a position to be helpful."

Added the Justice Department's Myron Marlin, "We are continuing to track every lead and take whatever preventive steps we can."

In Alexandria Bay, N.Y., the Customs Service closed the border crossing with Canada for three hours last night after dogs and a scanner indicated possible chemical residue in a vehicle, but inspectors concluded there were no explosives.

A woman upset over losing her job took at least two employees hostage for several hours inside a Kansas City area Bank of America branch before surrendering early this morning, but authorities said there was no indication that the incident was linked to any terrorism effort.

In New York, Mayor Rudolph W. Giuliani and Police Commissioner Howard Safir urged people to proceed with their holiday plans and avoid giving terrorists a psychological victory. "We have no specific credible threat that any terrorist is planning anything against New York City," Safir said. "But there are no guarantees."

New York police evacuated a crowd between 46th and 47th streets when a suspicious bag was found unattended Friday. Nothing dangerous was found inside. Later, a Michigan man who had aroused suspicion because he was carrying handcuffs was arrested after police found a loaded shotgun in his car in a parking garage on West 53rd Street. George James, 29, of Saranac, Mich., was charged with criminal possession of a weapon.

Also in New York, Abdel Ghani, an Algerian arrested on Thursday in Brooklyn and charged with playing a key role in the terrorist plot, shook his head during a court hearing where he was described as attempting to assist Ressam with the terrorist plot. After a U.S. magistrate ordered him held without bail, Ghani's attorney said it was pointless to seek bail because the government alleges Ghani is in the country illegally and lacks ties to the community.

According to a complaint filed in federal court in New York, Ghani has been under FBI surveillance since he traveled to Seattle several weeks ago with the intention of meeting Ressam. Ressam was to have left his rental car filled with powerful explosives and sophisticated timing devices in a parking lot, where another member of their terrorist network, possibly unknown to Ressam, would take charge of the vehicle.

But Ressam's arrest by U.S. Customs Service inspectors thwarted the plan. Ghani told a confidential informant that the plot was devised so that each person involved would only know the tasks of two others. Thus, in the event of an arrest, no one could expose the entire group, the FBI complaint said.

In recent weeks, FBI agents watched Ghani closely. They tracked him to Brooklyn after discovering his name and phone number on a piece of paper when they arrested Ressam. Within days, Ghani returned to New York--traveling under the alias Eduardo Rocha--and destroyed his plane ticket and a bank statement that would confirm his trip to Seattle.

About 10 days ago, FBI agents watched Ghani throw away several documents in a refuse bin near a Brooklyn supermarket close to the apartment where he was staying. Agents who recovered the papers said they included a Delta Airlines ticket receipt and itinerary from New York to Seattle, as well as ATM receipts from Seattle. A surveillance camera connected with one of the Seattle ATMs made a photograph of Ghani that matched a photo taken of him by agents conducting surveillance.

Meanwhile, Muslim leaders urged Americans not to overreact to the arrests of Ghani and the other Algerians. "The main concern from our standpoint is the mass hysteria resulting from the arrests," Salam Al-Marayati, director of the Muslim Public Affairs Council, told a gathering in Los Angeles. "At the same time, we're not shirking our responsibility and we're taking a strong stand against terrorism."

Collingwood said the FBI was not targeting people based on race or ethnic or religious ties. "I would hope people would understand we have an obligation to pursue investigative leads that develop," he said.

While federal investigators pursued large plans and organized plots, terrorism experts said the real security risks may lie elsewhere. Bruce Hoffman, a Washington-based terrorism expert at Rand, a think tank, said relatively small violent acts would be more difficult to prevent than those by international terrorists. Indeed, a large tower holding a line that carries electricity from Oregon to California was sabotaged and knocked over late Thursday, but no customers lost power because a computer quickly rerouted electricity.

Staff writer Liz Leyden in New York contributed to this report.

CAPTION: New York police leap barrier after evacuating a crowd in midtown Manhattan when a suspicious bag was left unattended. Nothing dangerous was found.