In documents filed Friday in federal court in San Francisco, prosecutors said Bobby Estalella, a onetime Giant who admitted to a federal grand jury that he got steroids from Bonds' trainer, and Kathy Hoskins, a former Bonds assistant who has known the slugger since childhood, would be key witnesses in Bonds' March 2 trial on perjury charges.

The holder of baseball's all-time home-run record and one of the greatest hitters in the history of the game, Bonds is accused of lying to a grand jury in 2003 when he said he had never knowingly used banned drugs. Bonds has pleaded not guilty.

In the documents, the prosecutors said they would call as many as 38 witnesses to try to make their case against Bonds - among them federal agents, scientists, doping experts, seven baseball players and one former NFL linebacker. All the athletes have admitted they obtained steroids from Bonds' trainer, Greg Anderson, as well as from BALCO, the Burlingame steroid lab at the center of a six-year federal probe of steroids and sports.

The prosecutors also said they want the testimony of a 39th witness - Anderson, who was convicted of steroid dealing in the Bay Area Laboratory Co-Operative scandal and then served a year in prison for contempt of court rather than give evidence about Bonds and banned drugs.

If Anderson refuses to testify at Bonds' trial, the prosecutors said they would ask Judge Susan Illston to hold him in contempt and put the trainer back in prison.

New injection claim

And for the first time, prosecutors said they have a witness who says she saw Bonds being injected by Anderson - Hoskins, who is also the sister of Bonds' former longtime business manager, Steve Hoskins, another key government witness.

In 2003, Steve Hoskins secretly tape-recorded a conversation in which Anderson described the regimen of undetectable drugs he was giving Bonds, the government says.

In Friday's filing, prosecutors did not assert that the injection Bonds allegedly received from Anderson contained banned drugs. Nevertheless, the claim is significant, because in his testimony before the grand jury that investigated BALCO, Bonds said he had never received an injection of any kind from Anderson, saying he had received injections only from doctors.

Ex-catcher's story

Estalella's claim that Bonds confessed to steroid use in "several discussions" also is new. In his own testimony before the grand jury that investigated the BALCO scandal, Estalella said he had gotten growth hormone and BALCO's undetectable steroids from Anderson, obtaining most of the drugs via express mail after he left the Giants in 2001 to play for the New York Yankees and Colorado Rockies.

But in that testimony, Estalella never claimed personal knowledge that Bonds himself was using banned drugs. Estalella, who retired from the game in 2004, first made the claim when reinterviewed by agents conducting the perjury investigation of Bonds, said a source familiar with the probe.

Three other former Giants - outfielders Marvin Benard and Armando Rios, and catcher Benito Santiago - are on the prosecution's witness list, as are three players with ties to the Oakland Athletics - designated hitter Jason Giambi, who just rejoined the team after a stint with the Yankees, and retired A's Jeremy Giambi and Randy Velarde.

None of them will claim personal knowledge of Bonds and steroids, according to the document. Instead, they will tell the jury that they received banned drugs from Anderson and BALCO.

That will also be the thrust of the testimony of former New England Patriot linebacker Larry Izzo, the lone NFL player on the prosecution's list, the government said.

Ex-girlfriend to testify

In a further effort to prove that Bonds used banned drugs, the prosecutors say they will also call Kim Bell, Bonds' former girlfriend. She will testify that before the 2000 baseball season, Bonds admitted to her that he was using steroids. She will also testify to observing physical changes in Bonds that the government will contend are consistent with steroid use - "acne on the shoulders and back, hair loss and testicle shrinkage," the documents say.

Bonds' defense team has long been prepared for some of this testimony. Michael Rains, one of Bonds' lawyers, has accused Bell of being a gold-digger who made up false accusations about the slugger in an effort to promote a tell-all book.

In 2003, Bonds himself told the FBI that Steve Hoskins had forged the slugger's autograph on bogus sports memorabilia and sold the items, although Hoskins' lawyer says he was exonerated after a probe.

But Bonds' defense team only recently learned that Hoskins' sister, who was a personal shopper and aide to Bonds, and who sometimes traveled with him on Giants road trips, also has emerged as a government witness.

Hoskins and his sister have known Bonds since their childhood on the Peninsula. They are the children of the late Bob Hoskins, a 49ers lineman of the 1960s who was a neighbor and close friend of Bobby Bonds, a former Giants outfielder and father of Barry Bonds.

E-mail Lance Williams at lwilliams@sfchronicle.com.

This article appeared on page A - 1 of the San Francisco Chronicle