WASHINGTON — Critics of a plan to send undercover air marshals to patrol trains, buses and ferries say it will take scarce resources away from airplanes and could get in the way of local police.

The Transportation Security Administration, in a little-noticed announcement on Tuesday, said teams of air marshals would begin counterterror surveillance on land as part of a small test program that also involves bomb-sniffing dogs and transit inspectors.

Beginning today, the teams were going out for three days at a bus station in Houston and at rail facilities in Baltimore, Washington, Los Angeles, Atlanta and Philadelphia.

Just hours before the undercover marshals arrived, Philadelphia police were told about the patrols for the local transit system, according to Rep. Allyson Schwartz, D-Pa.

Schwartz, who was briefed by Philadelphia and Southeastern Pennsylvania Transportation Authority law enforcement officials, said the TSA's failure to give advance warning was unacceptable.

"They said, 'We're coming in,' " Schwartz said. "They should at least have come in and said, 'How will it work best? Who do we call? How should we handle this?' "

TSA spokeswoman Yolanda Clark said the project was planned carefully and that local and transit police were notified about it last week.

James Carafano, a senior fellow at the conservative Heritage Foundation, said the point of the exercise was to figure out how federal counterterrorism officials could work with local police if terrorists threatened to attack transportation targets other than airplanes.

"These are pilot projects designed to figure out how do you do this," Carafano said.

Carafano said local police were right to be concerned about armed undercover law enforcement agents being assigned to their jurisdiction without adequate preparation.

But, he said, "the thought that air marshals are running around transit systems is a deterrent."

American Airlines pilot Denis Breslin, spokesman for the airline's pilots' union, said air marshals ought to stick to airplanes.

"I don't think there's enough air marshals to cover commercial aviation as it is," Breslin said. "That's what transit police are for."

Homeland Security Secretary Michael Chertoff, speaking in New York, said that aviation continues to be a priority.

Federal officials said they don't have any indication of a heightened threat toward other forms of transportation.

"There is no increased level of chatter through intelligence channels. Due to the time of the year, we intend to remain vigilant for any change in this posture," said FBI Special Agent Richard Kolko.

The tiny size of the test project — fewer than 60 people — is not expected to contribute much to counterterrorism efforts during the holidays.

There are, for example, about 3,700 police assigned to New York's Metropolitan Transit Authority. Amtrak has its own police force of 350 people and more than two dozen canine teams.

Thousands of air marshals were rushed into service after the Sept. 11 terrorist attacks. The service has been shunted among different agencies since then, starting out at the Federal Aviation Administration, moving to the TSA, then to Immigration and Custom Enforcement and, recently, back to the TSA.

Though the exact number of air marshals is classified, pilots estimate that they cover only a small percentage of flights. Efforts were made to expand coverage by cross-training other law enforcement officers to perform air marshal duties, but Congress put a stop to it.

Air marshals stepped outside of their usual role of flying undercover on airliners after Hurricane Katrina struck New Orleans. They were sent to keep order at Louis Armstrong International Airport, where thousands of evacuees converged after the levees were breached.

Air marshals last week shot and killed a passenger in Miami who they said made a bomb threat.

The Washington Post first reported the deployment of the VIPER teams.

On the Net: Transportation Security Administration: www.tsa.gov