PROVIDENCE — If former Senate President William V. Irons wins his court fight against the state Ethics Commission, it could cripple the commission’s ability to police unethical behavior in the General Assembly, a commission lawyer told a Superior Court judge yesterday.

Commission prosecutor Jason M. Gramitt said the commission would lose the ability to enforce rules against conflicts of interest and misuse of office, the most important parts of the state Code of Ethics.

He said the state’s voters clearly wanted to include the legislature in the commission’s jurisdiction in a 1986 amendment to the state Constitution, and that their decision grew out of public outrage against government corruption at the time.

Outside the courtroom, Gramitt said that under the rules Irons wants, many of the commission’s biggest ethics cases against powerful public officials would never have happened.

“Celona would have been out the window,” Gramitt said, referring to the case involving former state Sen. John A. Celona, whom the commission fined a record $130,000 in 2006 for ethics violations and who also ended up in prison on federal corruption charges.

So would the case against House Majority Leader Gordon Fox, Gramitt said. Fox paid a $10,000 fine in 2004 after acknowledging a conflict involving his role in winning a 20-year state lottery deal for GTECH, which assured that his law firm received legal work from the company.

Gramitt also said that success on Irons’ part could make it impossible for the state attorney general to prosecute legislators based on the most important role they play — voting.

Irons’ lawyer, John Tarantino, however, argued that the commission has no right to prosecute Irons at all, let alone punish him under the ethics charges against him — acting in conflict of interest and using his office for financial gain — because the charges rest on the way he voted.

Tarantino said the commission is trying to trespass on an important and longstanding legislative immunity from prosecution based in the Rhode Island and U.S. constitutions. He said that privilege, based on the almost identical “speech in debate” clauses in both documents, is intended to let legislatures act free from intimidation or any other outside interference — a critical protection of that branch of government.

“A legislator can’t be questioned for any legislative act,” Tarantino said, although legislators can be prosecuted for other misdeeds.

At the center of the legal battle is a 1986 amendment to the state Constitution that created the present Ethics Commission and included the General Assembly in its jurisdiction. Commission lawyers say it gives the commission unique power to enforce ethics rules on legislators. Tarantino says legislative privilege remains in force and trumps the amendment.

The fact that nobody challenged the commission’s jurisdiction between 1986 and the current dispute, Tarantino said, doesn’t make legislative privilege any less binding.

Tarantino, Gramitt and commission prosecutor Katherine D’Arezzo argued the case before Superior Court Judge Francis J. Darrigan. The judge made no immediate ruling, saying he will issue a written decision. He had told lawyers in the case that he might complete a decision within about two months, which would be relatively rapid compared with many other cases.

In addition to challenging the commission’s right to prosecute Irons, Tarantino also wants a jury trial, which the commission opposes. Under state law, the commission members now hold a trial-like hearing on the charges and decide the case themselves. Officials who are found guilty of violations can appeal commission decisions to the courts.

An East Providence Democrat in the insurance business, Irons resigned suddenly on Dec. 31, 2003, after being linked to a controversy involving undisclosed ties of a Senate ally, Celona, to the CVS drugstore chain and Blue Cross & Blue Shield of Rhode Island, the health insurer.

The Journal reported that Irons received $70,000 in commissions on a Blue Cross health-insurance policy for CVS employees in 2000 and 2001, and another $25,000 in 1999. Irons chaired the Senate Corporations Committee that handles health-care legislation, and opposed a controversial pharmacy-choice bill that Blue Cross and CVS also opposed.

The Ethics Commission argues that the 1986 Constitutional amendment that created the present Ethics Commission explicitly gave it unique authority to enforce the state Code of Ethics on the General Assembly. The amendment says that “all elected and appointed officials and employees of state and local government” fall under the Ethics Commission’s jurisdiction, seemingly including the General Assembly.

But Tarantino said that because the Constitutional Convention delegates didn’t explicitly set aside the legislators’ immunity under the “speech in debate” doctrine, that immunity continues and legislators can’t be prosecuted for the way they vote. That, he said, doesn’t “gut” the Ethics Commission’s enforcement power because it can enforce some provisions of the Ethics Code without relying on legislators’ votes to make its case.

Gramitt, however, quoted one of the 1986 convention delegates to say that, while Rhode Islanders may like their individual senators and representatives, “We don’t trust the legislature” as a whole.

The convention delegates, Gramitt said, knew exactly what they were doing: making an exception for the Ethics Commission so it could impose ethics standards on legislators along with other officials.

blandis@projo.com