LOS ANGELES, Dec. 20 — Police have found the gun believed used in the slayings of three of the five victims in the Tate murder case, it was learned Friday.

The long-barreled .22-caliber handgun reportedly was located earlier in the week near the area where a television news team Monday found clothes which police reportedly have established were worn by the killers.

The general location where the clothes — three black T-shirts, one white T-shirt and three pairs of black jeans — were found was revealed by Susan Denise Atkins, one of those indicted for the crimes and the prosecution’s key witness before the grand jury.

It earlier had been indicated that police had found a piece of the handle from the murder weapon in the Tate home. The same piece reportedly fits the weapon found this week.

Both the clothing and the weapon are said to have been found near the Benedict Canyon estate where actress Sharon Tate and four others were slain.

Since locating the weapon, police have been attempting to establish whether it matches the bullets taken from the bodies of hair stylist Jay Sebring, Polish playboy Wojciech (Voityck) Frykowski and Steven Parent.

Sebring and Frykowski were stabbed and shot to death at the Tate home, while Parent was killed as he was leaving the estate after having visited the caretaker.

Miss Tate and coffee heiress Abigail Folger were stabbed, but were not shot.

Charles M. Manson, leader of a hippie cult, and four of his followers are charged with conspiracy arid murder in the Aug. 9 Tate slaying.

They also are accused, along with Leslie Van Houten, of murdering Leno LaBianca and his wife, Rosemary, the following day in their Los Feliz area home. The LaBiancas were repeatedly stabbed.

Miss Van Houten appeared in court Friday to hear Superior Judge William B. Keene appoint Marvin L. Part as her attorney.

Part, a former deputy district attorney, was named to replace Donald Barnett, who previously indicated that he was hired by Miss Van Houten’s family to represent her.

After Barnett notified the court that the 19-year-old defendant’s parents lacked the funds to pay an attorney and Miss Van Houten said she wanted a different lawyer, Judge Keene selected Part, who has more than 10 years experience in handling criminal matters, most of it as a prosecutor.

Two of those charged with the Tate and LaBianca slayings still have not been returned to Los Angeles.

Charles D. (Tex) Watson is scheduled to appear on Jan. 5 in Austin, Tex., for a governor’s hearing at which Watson will oppose extradition.

Patricia Krenwinkel was arraigned Friday in Mobile, Ala., on a fugitive warrant and was given until Dec. 29 to decide whether she will continue to fight extradition to California. She is being held in the Mobile County Jail.

Meanwhile, it also has been learned that Miss Atkins has denied knowledge of 30 unsolved murders in California since 1968 in which the victims were killed under circumstances similar to those in the Tate and LaBianca cases.

The unsolved slayings include the Aug. 5 stabbings of two San Jose, teenage girls and the Jan. 1 murder of Marina Habe, 17, in the Hollywood Hills.