Federal law enforcement officers who accept free rides in exchange for providing security aboard Maryland's regional commuter trains are not violating ethics rules, according to the federal government's chief ethics officer.

Federal agencies should consider, however, whether such arrangements raise liability issues or run afoul of agency-level policies on employees' outside activities, Marilyn L. Glynn, acting director of the U.S. Office of Government Ethics, wrote in a July 7 memo.

Glynn's memo to agency ethics officials, general counsels and inspectors general addressed potential concerns about the MARC Sworn Officer Program. The initiative, begun in January 2003, allows local, state and federal law enforcement personnel to ride MARC trains at no charge -- as long as they consent to serve as armed undercover security officers along the route. The Virginia Railway Express began a similar program in February 2002, offering free passage to any law enforcement officer who agrees to respond to a felony on a train or in a station.

"The offer of free ridership does not appear to be gratuitous, as participating law enforcement personnel must agree to provide certain security-related services in exchange," Glynn wrote, referring specifically to the Maryland program. "Consequently, we believe that this program is best viewed as a type of employment or services agreement, rather than as a gift subject to" ethics rules.

Vincent J. Salamone, associate general counsel at the ethics office, cited office policy and declined to speak on the record about Glynn's memo. He would not say whether it also applies to the Virginia program.

More than 9o percent of the 95 law enforcement officers in the MARC program work for the federal government, said Richard Scher, a spokesman for the Maryland Transit Administration. Participants have a special stamp on their train passes and hail from a variety of agencies, including the U.S. Customs and Border Protection bureau and the U.S. Marshals Service, Scher said.

"The best surveillance system that transit agencies have are the eyes and ears of riders," he said.

The Virginia program has 135 participants, the most it can accept, said Mark Roeber, a VRE spokesman. About 92 percent are federal employees. Undercover officers carry train passes bearing a special code so VRE officials can identify them.

So far no officer has had to make an arrest, Roeber said. He said liability for injuries or damage caused while making an arrest or stopping a felony "falls to us," not the officer or his home agency.

"It's a great program for us because it provides a highly sophisticated level of protection while not having us have to incur the cost of spending hundreds of thousands of dollars for security personnel," Roeber said.

And it can save law enforcement officials a few bucks on their commute. An officer who lives in Woodbridge, for instance, normally would pay $171.70 for a monthly pass to Union Station and back. A MARC train rider commuting to Washington from Gaithersburg would fork over $125 for an unlimited monthly pass.

Louis P. Cannon, president of the District of Columbia Lodge of the Fraternal Order of Police, said he was unaware of the programs until contacted by a reporter last week.

"We would certainly be happy to promote it through our membership. I don't think you would have any problem with the officers volunteering to do that," said Cannon, whose organization represents 10,000 law enforcement officials in municipal and federal agencies.

Cannon, an inspector with the Treasury Department's U.S. Mint Police, said he lives a few miles from a MARC station and might join the program.