SAN FRANCISCO -- Barry Bonds' personal trainer refused to tell a grand jury Thursday whether he gave the slugger steroids, but a federal judge rejected a prosecution request to jail Greg Anderson for contempt of court.

U.S. District Judge William Alsup said he must review the transcript of the brief grand jury hearing and hear arguments from lawyers before deciding if Anderson should go back to jail. He ordered Anderson, 40, to return to court Aug. 28.

The contempt hearing was the first time prosecutors publicly revealed they are targeting Bonds in a performance-enhancing drug probe linked to some of the world's top athletes, including Yankees star Jason Giambi and sprinter Tim Montgomery.

On Anderson's fifth appearance before a federal grand jury, he answered basic questions, including his name, prosecutors said. Until now, he had answered no questions.

But federal prosecutors said Anderson didn't answer any substantive questions about steroids and that his answers were designed to delay the process, Assistant U.S. Attorney Matthew Parrella argued.

"This was a more cynical appearance than any before," Parrella said.

For instance, Anderson refused to answer when Parrella asked, "Did you distribute anabolic steroids to Barry Bonds?"

That was the first public acknowledgment that Bonds, second on major league baseball's all-time home run list, is the target of a grand jury investigation.

All other reports have been based on leaked copies of grand jury transcripts in the investigation of the Bay Area Laboratory Co-Operative that netted five convictions for steroid distribution. Several elite athletes testified about their steroid use and Parrella told the judge the new investigation involved whether "some of those athletes committed perjury and/or obstructed justice."

Parrella said prosecutors want Anderson to explain calendars with doping schedules and other evidence seized from his house.

Despite the government's insistence that Anderson essentially refused to testify yet again, Alsup allowed the trainer to go free until transcripts could be produced and distributed to lawyers on both sides.

Alsup also allowed Anderson's attorney Mark Geragos to make one last argument for why his client shouldn't have to testify. Geragos lost those arguments July 5 when Anderson was initially jailed for refusing to testify.

"There is a substantial difference between this time and last time," Geragos said.

Numerous grand jury leaks have left Anderson mistrustful that his testimony will be kept confidential, Geragos said. It would violate a deal struck in December to plead guilty to steroids distribution and money laundering, in which Anderson specifically stated he would not cooperate with the government.

But Alsup has already rejected those arguments as well as a third claim Geragos intends to renew, which is that Anderson was a target of an illegal wiretap. A federal appeals court also rejected the wiretap argument.

Anderson spent 15 days in prison last month for refusing to testify, but was freed after that grand jury's term expired.

He also served three months in prison and three months of home detention after pleading guilty to steroid distribution and money laundering stemming from the government's investigation of BALCO, which allegedly supplied Bonds and other athletes with performance-enhancing drugs.

Government lawyers are investigating whether Bonds lied under oath when he told an earlier grand jury he didn't know whether the substances Anderson gave him were steroids.

The grand jury investigation also reportedly is focused on whether the San Francisco Giants outfielder paid taxes on the sale of hundreds of thousands of dollars worth of sports memorabilia.

The New York Times reported last month that the grand jury is also looking into the possible involvement of Trevor Graham, the track coach of sprinters Marion Jones and Justin Gatlin. Gatlin, 100-meter co-world record holder, tested positive this year for elevated testosterone.

Some legal experts see Anderson as the key to proving the perjury allegations, since Bonds reportedly testified the trainer gave him two substances that fit the description of "the cream" and "the clear" -- two drugs linked to BALCO.

In 2003, Bonds reportedly testified to the grand jury investigating BALCO that he believed the substances were flaxseed oil and arthritis balm, not steroids.

Anderson also could tell why Bonds' name appears on doping calendars seized during a raid at the trainer's house, according to court papers.

Anderson's not the only one facing jail time for refusing to testify. San Francisco Chronicle reporters Lance Williams and Mark Fainaru-Wada were ordered to name the sources who leaked grand jury transcripts they used to write a book on Bonds' and his alleged steroid use.

The reporters have said they would go to jail rather than reveal their source or sources.