SANTA CRUZ, Aug. 21 — Lynette “Squeaky” Fromme, convicted of trying to assassinate President Ford, has told Susan Murphy, a fellow follower of Charles Manson, “you’d best realize your life is on the line, and not because of the FBI.”

The search for Miss Murphy, who escaped from federal prison a week ago, widened today after authorities disclosed she had been treated in a Santa Cruz hospital two days after the breakout.

Miss Fromme, a former roommate of Miss Murphy, phoned The Associated Press in San Diego yesterday and said she wanted to send a message to Miss Murphy. She then read this statement:

“You are not Manson family but you carry that name. I wish you well, but you’d best realize your life is on the line, and not because of the FBI.

“This family is for earth balance, not money, dope or power plays.”

Miss Fromme declined to explain what she meant in the statement. The phone company confirmed that the call came from the Metropolitan Correctional Center where Miss Fromme is serving a life sentence for the attempted assassination of Ford.

FBI spokesman Frank Perrone said yesterday that Miss Murphy, 34, had been treated for an undisclosed ailment at the Santa Cruz Community Hospital Monday. He said she paid for the treatment with a check taken from a prison guard in the escape.

He said the search for Miss Murphy and another prison escapee had centered on the San Francisco Bay Area since the pair rented a car here and apparently abandoned it in San Jose.

Miss Murphy was convicted with “family” member Sandra Good of conspiring to write threatening letters to business executives whom they accused of polluting the environment.