A majority of U.S. Supreme Court justices questioned the legitimacy of defunct accounting firm Arthur Andersen’s conviction for obstructing an investigation into energy trader Enron.

Andersen’s lawyer said the firm shouldn’t have been convicted for urging its employees to destroy documents before the Securities and Exchange Commission began investigating Enron audits. The government’s lawyer said that telling workers to purge records was illegal if there was a “reasonable possibility”of an investigation.

“You want criminal liability to turn upon that?” Justice Scalia asked Deputy U.S. Solicitor General Michael R. Dreeben. The justice said it would mean that telling employees to destroy documents was illegal while the actual destruction of records was legal under federal law at the time. “Doesn’t that seem strange to you?” Mr. Scalia said. The court will rule by July.

The 2002 conviction of Andersen, once the world’s fifth-largest accounting firm, forced it to stop conducting public audits and led to its collapse from 85,000 employees to fewer than 200. Andersen was the auditor for 16 years for Enron, whose bankruptcy in 2001 marked the beginning of corporate scandals and a wave of criminal trials of executives. Yesterday’s argument was the last of the court’s 2004-05 term.

Though a high court ruling overturning Andersen’s conviction by a federal jury in Houston wouldn’t restore the firm’s standing in the accounting world, a victory would be a boost for Andersen’s former partners as they try to resolve civil lawsuits seeking billions of dollars. A ruling for Andersen also would throw out a $500,000 fine the firm was ordered to pay.

Andersen said in a statement yesterday that a decision voiding its conviction would be “tremendously significant” for the firm and tens of thousands of former partners and employees.

The prosecution “was unjustified and the ensuing collapse of Arthur Andersen was an undeserved tragedy – for its employees, clients and the business community at large,” the statement said.

Andersen’s Enron team destroyed almost two tons of paper and tens of thousands of e-mails, the government said.

Mr. Dreeben compared the document purging, which lasted until the SEC served a subpoena for records, with someone at a crime scene wiping away fingerprints before the police arrived.

Andersen was “seeing the SEC coming down the pike,” said Mr. Dreeben, who said the firm didn’t purge the documents because it was “preoccupied with neatness.”

Also questioning Andersen’s conviction were Justices O’Connor, Breyer, Kennedy and Souter.

Ms. O’Connor suggested that the federal Sarbanes-Oxley Act, enacted in 2002 to tighten the rules governing corporate finances, “comes closer to the mark” of covering the conduct that led to Andersen’s conviction.

Mr. Breyer said federal criminal laws tend to be written narrowly to make clear what conduct is unlawful.

“Doesn’t that tend to cut against you in this case?” Mr. Breyer asked Mr. Dreeben.

“How’s the business person to know what they can do?” added Ms. O’Connor. “How’s the lawyer to know what they can do?”

Mr. Dreeben said the jury was correctly told it was illegal to destroy a document with the intent to “subvert, undermine, or impede” an official proceeding.

“That is a sweeping provision that may cause problems for any company or small business in the country,” Mr. Kennedy said. Mr. Souter said the word “impede” is “getting pretty thin on knowledge of wrongdoing.”

Enron, once the world’s largest energy trader, sought bankruptcy protection in 2001 following disclosures that it hid billions of dollars of debt in offbook partnerships.

Andersen wasn’t charged for the document-destruction itself. Instead, the government prosecuted Andersen under a federal witness-tampering law that made it a crime to “corruptly” persuade someone to destroy evidence.

Andersen said it destroyed Enron records as part of a “document retention” policy to eliminate duplicates, drafts, and notes once an audit was complete. Prosecutors said Andersen ignored the document-handling policy until the firm realized an SEC investigation into its Enron audits was likely.

Andersen lawyer Maureen E. Mahoney said the government’s interpretation of the law “covers a full range of conduct that is unquestionably innocent.”

Andersen officials believed their actions were legal when they instructed employees to follow the document handling policy, Ms. Mahoney said. She said in-house attorney Nancy Temple was giving legal advice allowed under the law.

David Duncan, the former head of Andersen’s audit team who later pleaded guilty to obstruction and testified in the company’s criminal trial, said he hadn’t believed at the time he was doing anything illegal, Ms. Mahoney said.

Justice Ginsburg asked about Andersen partner Michael Odom, who told employees that, if they destroyed a document the day before litigation is filed, “that’s great.” Ms. Mahoney said that was a correct interpretation of the law in effect.

A federal judge Tuesday granted preliminary approval of Andersen’s agreement to pay $65 million to settle claims stemming from the 2002 collapse of WorldCom, another former Andersen client.