LOS ANGELES, Mar. 19 – As anticipated, Linda Kasabian has agreed to testify for the prosecution against Charles Manson and four other co-defendants in the Tate-LaBianca murders, it was learned Wednesday.

Attorneys for Mrs. Kasabian’s co-defendants have known for weeks that her lawyers were seeking promises from the district attorney’s office in exchange for her testimony.

Negotiations between prosecutors and her lawyers, Gary B. Fleischman and Ronald Goldman, reportedly began immediately upon her return here after her December arrest in New Hampshire.

However, Dep. Dist. Attys. Aaron Stovitz and Vincent Bugliosi denied a report Wednesday that she has been granted immunity from prosecution.

They declined comment when asked whether she might eventually receive immunity if she cooperated in the prosecution of her co-defendants.

It is known, however, that Mrs. Kasabian has been told if she truthfully relates in court what she knows about the August murders, prosecutors have promised to intercede in her behalf with the trial judge.

Immunity commonly is granted only after a witness lives up to his or her part of the bargain during a trial. After the trial ends, an immunity order must be signed by the trial judge at the request of the prosecution.

To obtain Mrs. Kasabian’s cooperation, prosecutors also would have to sever her case from that of Manson and the other four.

Such a severance appears to be in the works, as the following evidence of Mrs. Kasabian’s apparent willingness to cooperate with the prosecution indicates:

— As early as Feb. 28, Bugliosi was seen entering the Sybil Brand Institute, where she was being held, with one of her lawyers.

— The same day, she reportedly was taken to the scene of the Tate slayings, the Benedict Canyon estate where five persons were killed Aug. 9.

— Sunday, Bugliosi took her to the site of the LaBianca slayings in the Los Feliz district.

An early hint that Mrs. Kasabian was prepared to cooperate with the prosecution came Jan. 20 when her attorneys indicated that she wanted no part of the “common defense” proposed by Manson.

In an unsuccessful effort to win her release on bail, they argued that she accompanied the others on the August forays only because she feared for the life of her 2-year-old daughter.

Her lawyers said that on the nights of the killings she had no choice but to leave the child, Tanya, at the Spahn Ranch and comply with the orders of Manson and Charles (Tex) Watson.

Since then, Mrs. Kasabian has given birth to a son. Her attorneys have steadfastly refused to permit members of the Manson family to visit her in jail or the hospital. She also has been under heavy guard.

Evidence against Mrs. Kasabian — including Susan Atkins’ testimony before the grand jury — has been less damning than against any of the others accused, it was learned.

According to Miss Atkins’ grand jury testimony, Mrs. Kasabian never entered the Tate mansion and rode away in a car from the LaBianca residence before that couple were murdered.

While negotiations for her to turn prosecution witness reportedly began in December, they were believed stepped up a few weeks ago when Miss Atkins insisted on conferring with Manson.

Acting as his own attorney at the time, he had authority to speak with her in jail as a prospective defense “witness.”

After that meeting, Miss Atkins’ attorney, Daye Shinn, said she would repudiate her grand jury testimony and would not testify.

It is understood that prosecutors feared even before Miss Atkins’ jailhouse confrontation with Manson that once they were reunited, the prosecution could no longer rely on Miss Atkins as a witness.

The prospect that Miss Atkins would not repeat her grand jury story before a trial jury made Mrs. Kasabian’s cooperation extremely important to the prosecution, it is understood.

She can tell basically the same story, it is believed, as that of Miss Atkins — with one critical exception.

Since she apparently was not present in the Tate residence or on the mansion grounds during the killings, she cannot describe them as Miss Atkins did before the grand jurors.

By JERRY COHEN and RON ELNSTOSS