By Dan Levine

SAN FRANCISCO (Reuters) - A judge should not overturn a jury verdict against baseball home run king Barry Bonds relating to an investigation of steroids in sports, a U.S. prosecutor argued in a hearing on Thursday.

Bonds was convicted in April by a Northern California jury on a single count of obstruction of justice in a scandal over performance-enhancing drugs that has tarnished some of the biggest stars in baseball.

The jury deadlocked on three other counts of lying to a grand jury. All the charges stemmed from Bonds' testimony to a 2003 grand jury investigating the Bay Area Laboratory Co-operative, or BALCO.

Testifying to the grand jury, Bonds admitted getting flaxseed oil, vitamins, protein shakes and creams from his trainer, but said he had no knowledge of human growth hormones or steroids. He said no one ever injected him other than medical doctors.

The government maintains that Bonds obstructed justice in response to a question about whether his trainer ever gave him anything that required a syringe. Defense attorneys for the slugger have asked that the one conviction be thrown out, or that the charge be retried.

In a San Francisco federal court on Thursday, assistant U.S. Attorney Merry Jean Chan argued that Bonds was asked a very specific question about injections, but did not directly answer.

"He could have said yes or no," Chan said.

Dennis Riordan, an attorney for Bonds, urged U.S. District Judge Susan Illston to focus on Bonds' single answer during his grand jury testimony.

Illston, however, said it seemed necessary to evaluate all the evidence in the trial to decide whether the obstruction conviction should be overturned.

"I don't think it's fair to say, just focus on the one statement," Illston said.

The judge did not rule from the bench on Thursday, but said she would issue a written order in the future.

U.S. prosecutors could eventually decide to retry Bonds on the three counts on which the jury deadlocked.

Illston previously told lawyers that the government should not have to decide whether to retry the three unresolved charges until the fate of the conviction was clear.

Bonds was the National League's most valuable player seven times and finished his career in 2007 with 762 home runs, most in the history of Major League Baseball. Bonds, who spent much of his career with the San Francisco Giants, also set the single-season home run record with 73 in 2001.

He was indicted three months after breaking Hank Aaron's career homer record in 2007.

The case in U.S. District Court, Northern District of California is United States of America v. Barry Lamar Bonds, 07-cr-0732.

(Editing by Jerry Norton)