Prosecutors asking lawmakers to keep their hands off an investigation into Ohio's government scandal have legitimate concerns over compromising their case.

A task force of county and federal prosecutors want top lawmakers to avoid hearings on the scandal out of fear such hearings could provide immunity from criminal prosecution.

An investigation that began with revelations of a $50 million investment in rare coins by the state insurance fund for injured workers spawned numerous other inquiries, including one of Gov. Bob Taft's illegal acceptance of free golf and other gifts.

Taft, a Republican, pleaded no contest to four ethics charges last month, becoming the first Ohio governor charged with or convicted of a crime. Lawmakers want to find out what happened and how to prevent similar problems, while prosecutors want to punish someone, said Dean Carro, a University of Akron law professor.

''The prosecution's worried about the Legislature trying to fix something for the future, and compromising their ability to prosecute for a past act,'' Carro said.

Legislative hearings are ''a very effective tool for legislators,'' said Ohio State University law professor Sharon Davies. ''It just is one that happens to create problems for prosecutors.''

In a letter to top legislative leaders last week, the prosecutors and the Ohio Inspector General say they're worried about a state law that gives witnesses at legislative hearings immunity in exchange for testimony.

The hearings ''could allow certain suspects to escape prosecution entirely,'' say the prosecutors, who include an elected Democrat, an elected Republican and two federal prosecutors appointed by President Bush.

Republican leaders of the GOP-dominated Legislature called for a committee in June - with subpoena powers - to review policies and procedures at the Ohio Bureau of Workers' Compensation.

Democrats say there's a way to get around the immunity issue raised by prosecutors by agreeing on who should or shouldn't be asked to testify.

''How many millions of dollars worth of contracts are going to be bought and sold to the highest campaign contributor at the Statehouse before this Legislature takes action?'' said Rep. Chris Redfern of Port Clinton, the highest-ranking House Democrat.

Senate President Bill Harris, citing the prosecutors' request, rejected that approach last week and said he wants to hold off on convening any committee, including the one he pitched in June.

''I want bad actors who have violated the public trust to be prosecuted to the fullest extent of the law,'' said Harris, an Ashland Republican. ''What I will not do is cave into political pressure and start this process until I have a complete picture of what the problem is.''

In 1990, a federal court ruled the government could not prosecute Oliver North for his role in the Iran/Contra scandal because prosecutors couldn't prove they didn't make use of his immunized testimony before Congress.

In 1991, a federal court reversed the Iran/Contra-related conviction of former National Security Adviser John Poindexter on similar grounds.

And in 1990 in Ohio, the state Supreme Court reversed the conviction of Pam Conrad, former finance director for the Ohio Democratic Party.

The court's 4-3 decision cited testimony she gave to a legislative committee investigating allegations that the administration of then-Gov. Richard Celeste traded state contracts for political contributions.

The prosecutors' concerns are understandable given those precedents, said Christo Lassiter, a University of Cincinnati law professor.

''No matter how many times a witness is prepared, and tries to speak truthfully, it's almost a guarantee that if you give a story twice, it won't be same,'' he said. ''That's going to be tremendous fodder for defense counsel in impeaching witnesses later.''

Andrew Welsh-Huggins is a statehouse correspondent for the Ohio Associated Press' Columbus bureau.