Riders on virtually all Amtrak trains that pass through New York's Penn Station must reserve tickets in advance during the Republican National Convention, which runs from Sunday to Thursday, officials said, regardless of whether passengers are going to the city.

Amtrak officials said trains would be swept by police and bomb-sniffing dogs before they leave stations and that sweeps also would take place en route as part of several security measures instituted for the convention. Riders should expect delays "in terms of minutes rather than hours" because of the sweeps, the officials said.

The Transportation Security Administration also will screen all bags checked at Penn Station, and authorities will more stringently enforce a requirement that riders put their names and addresses on luggage.

"We want to be able to associate bags with individuals for security reasons" in case the dogs find anything suspicious, Amtrak spokesman Cliff Black said.

The tactics include some security policies instituted after the terrorist attacks of Sept. 11, 2001, although officials said they would be enforced more vigorously during a convention that is considered to be a ripe target for terrorists. In general, safety on the nation's trains has received heightened attention since March 11, when a terrorist attack on a commuter train in Madrid killed nearly 200 people and injured 2,000 others.

Amtrak officials said the reservations-only policy is designed to gauge the size of crowds expected on trains and in Penn Station, which sits under Madison Square Garden, the site of the convention. Officials said knowing crowd sizes will determine how many train cars they will use and how to direct foot traffic in the station, where only two of eight entrances will be open because of security concerns there.

"This is not a security measure as much as an inventory for us to size our trains to adequately handle the crowds," Black said. The policy would give officials a list of all riders, "but we don't compare that to a watch list" like airlines, he said. The list would provide a useful database if an attack occurred, officials acknowledged.

Black said the only Amtrak lines that customers could still board before getting a ticket would be the Keystone and Clocker commuter lines that start in Pennsylvania and stop in New Jersey on their way to Penn Station.

"They are populated largely by daily commuters, and those daily commuters hold monthly tickets," Black said. He added that officials saw no reason to "make them go through the hassle of making reservations and buying tickets for each day of travel."

Black noted that some New Jersey and Long Island transit lines also will not require reservations during the convention.

About half of Amtrak's Northeast corridor trains, including its popular Acela and Metroliner services, already require reservations. Officials noted that a reservations-only policy has been instituted over Thanksgiving weekend for the past two years, helping to spread out heavy crowds. The policy means that a seat would have to be reserved even if a passenger is traveling from the District's Union Station and getting off before New York.

David Johnson, assistant director of the National Association of Railroad Passengers, said riders were "pleased with steps Amtrak has taken for the Republican convention. We understand Amtrak is doing it to control crowding conditions, thus making security sweeps and other security measures easier."

New York Police Department Emergency Services Unit members keep watch at Penn Station.