By Peter Henderson

SAN FRANCISCO (Reuters) - A U.S. judge on Friday considered whether to throw out government evidence in the perjury case of Barry Bonds, a day after prosecutors dropped more than half the charges against the home run king.

The government in a new indictment charged Bonds with four counts of lying to a grand jury about his use of performance-enhancing drugs and one count of obstruction of justice. It dropped six other perjury charges based on the same testimony.

If convicted, Bonds would still face a maximum of a decade in jail on each count, though U.S. District Judge Susan Illston could decide to sentence him to far less time.

Bonds was given immunity from prosecution for his testimony in the Bay Area Laboratory Cooperative, or BALCO, steroids scandal case, but the immunity did not cover lying to the grand jury.

The trial begins March 21, and Illston considered on Friday whether a recording of an expletive-filled conversation about drug testing, Bonds and injections may be used by the government.

She did not signal her decision in the short hearing that also included discussion of jury instructions and procedural matters.

Neither man in the conversation, Bonds' former personal trainer Greg Anderson nor the star's business associate Steve Hoskins, who recorded the conversation, clearly or directly says Bonds took steroids.

Early in the three-part conversation, Hoskins says "Barry was taking those shots." And in another section Anderson says in the context of drug tests "... everything that I've been doing at this point, it's all undetectable."

Illston has already rejected government plans to use coded drug tests and calendars that prosecutors said showed Bonds used steroids.

Bonds passed Hank Aaron to become Major League Baseball's career home run leader in 2007, but the record was tarnished the same year by a federal indictment charging he lied about use of performance-enhancing drugs.

A government investigation of Northern California's BALCO led to its founder Victor Conte admitting to being guilty of steroid distribution in July 2005 in a plea deal.

(Editing by Philip Barbara)