Actors lucky enough to land bit roles playing New York police officers on television may have to start being more careful about how they get to work.

With security tighter in the Big Apple since the terrorist attacks on September 11, 2001, the union that represents TV and film actors has begun advising its New York-area members to stop buying police costumes or carrying them to gigs, even if their performances require them.

The Screen Actors Guild said in a statement posted on its Web site on Friday that “an apparent shift in city policy” may put actors at risk of arrest if they are stopped while carrying anything that looks too much like a real police uniform.

The odds that an actor might be stopped and questioned on his or her way to work went up this month when police began conducting random searches of passengers’ bags in New York’s subway system. The guild said two of its members had been detained by security personnel at an airport and a courthouse in recent months for possessing police costumes.

City code has long prohibited anyone other than a police officer from possessing a replica uniform or badge. But guild spokesman Seth Oster said yesterday that actors have traditionally been able to obtain letters from the police commissioner giving them permission to carry such items to work on the sets of movies or shows like NBC’s “Law & Order.”

New York Police Department spokesman Paul Browne said that practice was abolished after the 2001 terrorist attack and has not been revived.