Fan mail — that old barometer of an entertainer's popularity — has become off-limits for many in Hollywood since the anthrax mail attacks in New York City, Washington and Florida. 

Studios, networks and publicists say thousands of letters have been returned to sender or just set aside. Some celebrities have signed up with services that open fan-mail for them; others have simply stopped opening mail.

``For the time being, we are just not opening fan mail. Just to be careful, we are putting it off for now,'' said publicist Pat Kingsley, who represents actor Tom Cruise, among others.

Thousands of unsolicited letters pour in to celebrities every week. Although most are simple declarations of admiration, precautions have long been taken to check for suspicious letters and packages.

``There is always a concern with celebrity fan mail because it comes from unknown people. But anthrax has added a new element,'' said PMK publicist Tracy Shaffer, who represents such acts as singers Evan and Jaron.

The FBI has not received a specific threat related to celebrity mail, said Cheryl Mimura, an FBI spokeswoman in Los Angeles.

``We haven't sent out any sort of advisory in Hollywood,'' she said.

Shaffer said some of her clients contacted her after a letter containing anthrax was received in the New York office of NBC anchor Tom Brokaw.

``We are directing our clients to use fan-mail services,'' she said. Such services open mail for celebrities, and return photographs and autographs to fans.

Studio Fan Mail Services, one of the oldest and largest fan-mail services in the country, has begun advising fans to send postcards rather than letters.

``Most of the mail our clients get is from children. We're telling them to write a postcard. That way they can still send their message,'' said owner Jack Tamkin.

Others suggest e-mail.

``We are returning fan letters and sending a note along asking them to correspond by e-mail,'' said Scott Rowe, Warner Bros. vice president of communications. Movie studios and TV networks receive the bulk of fan mail, and some have stopped delivering it.

Rocker Pat Benatar said she always was careful with fan mail and ``I'm trying really hard not to wig out on this. I'm trying to keep a perspective on it. But when we get the mail I'm careful about it. I tell my children not to touch it.''

Fan mail is important to many actors and celebrities.

``It's somebody that takes time to buy a card or get a piece of paper and pencil, collect some thoughts and put them on a piece of paper. That means something,'' said David Brokaw, who along with his brother Sanford make up the Brokaw Co., which represents Bill Cosby among others.

Brokaw would not comment on mailroom procedures implemented because of the anthrax scare.

``We are being vigilant. But I also say we are by no means hysterical about it,'' he said.

Soap-opera actor Steve Blackwood is no stranger to threatening letters. Playing bad-boy Bart on NBC's ``Days of Our Lives,'' he said fans sometimes confuse him with his character. Typically, he has ignored such letters. But recently he received one that left him feeling uneasy.

``In two previous story lines, we blew up a restaurant and we blew up a part of fictional Salem. I get this letter that says, 'How do you feel about giving terrorists ideas,''' he said. ``I got kind of spooked.''

Blackwood said he has stopped opening fan mail at home.

``For now, we just have to take precautions and ride it out,'' he said.