A reporter at the Keene, N.H., Sentinel recently got a call from a man who said his name was Jerry Stein, and that he worked for the Anti-Defamation League of the B'nai B'rith."Stein" said he was concerned about the reputed anti-Semitic tendencies of a Lyndon H. LaRouche, the former U.S. Labor Party head now running for the Democratic presidential nomination, and asked what sort of "bad news" the paper had printed about him.

The reporter later called the A.D.L. No one named Jerry Stein was working there.

Scores of mysterious phone calls have been received over the past few weeks by reporters, Democratic Party and campaign workers involved in the Feb. 26 primary campaign. In each case the pattern is the same: the caller identified himself, and asks questions about LaRouche. A call to the organization reveals no such person exists.

The result is suspicious, campaign workers, reporters and party officials now routinely refuse to talk with a caller until confirming the person's identity.

"I'm sorry," said one party official to a reporter yesterday, "but I don't talk to anyone about LaRouche on the phone anymore until I know who they are."

Many of the callers use Jewish surnames and ask questions about LaRouche's supposed anti-Semitism. Sometimes they do not identify themselves, but ask simplistic questions.

"I get at least two calls a week from these people," said Carol Carson, who runs a senior citizen center in New Hampshire. "If someone calls and asks what the name of the head of the American Association for Retired People is, I know it's a LaRouchie."

The "LaRouchies," as that campaign's workers have been dubbed, deny their people are responsible. "It's a Byzantine dirty trick," said LaRouche spokeswoman Laura Cohen. "I cannot swear that there was never anyone who did anything like that, but as an organization we don't do it and it's not true."

She said the LaRouche campaign has been victimized by dirty tricks, and she also said LaRouche has been targeted for assassination. LaRouche, 57, is guarded by private armed guards wherever he goes.

Democratic Party officials complain that LaRouche workers harass them and others with calls and other tactics.

"They stand at traffic lights with their literature and thrust it into the car when the light is red," said Patricia McMahon, executive director of the New Hampshire Democratic Committee. "They force it on you, they're so aggressive. And they're continually calling here asking for the same information over and over. They're pests."

She has gotten calls from a "reporter" for the University of New Hampshire newspaper and from someone who said he was Howard Blum, a New York Times reporter who wrote and expose of the U.S. Labor Party and LaRouche last fall. The number "Blum" gave her turned out to be that of a New York advertising agency.

"It's Donald Segretti type stunts," said one Democrat. "It isn't illegal. But it sure is annoying."