WASHINGTON (Reuters) - U.S. Supreme Court nominee Samuel Alito, seeking to avert a possible controversy, said on Thursday he never to his knowledge ruled in a case in which he had an obligation to recuse himself -- and had been "unduly restrictive" in a 1990 vow on possible conflicts of interest.

"I have been committed to carrying out my duties ... in accordance with both the letter and spirit of all applicable rules of ethics and canons of conduct," Alito, a federal appeals judge, wrote Senate Judiciary Committee Chairman Arlen Specter, a Pennsylvania Republican

"To my knowledge, I have not ruled in a case for which I had a legal or ethical obligation to recuse myself during my 15 years on the federal bench," Alito wrote.

Specter urged Alito earlier in the day to respond after recent Democratic questions about the ethics of President George W. Bush's conservative nominee to the nation's highest court.

If confirmed, Alito would replace retiring Justice Sandra Day O'Connor, a more moderate conservative who has often been the nine-member court's swing vote on hot-button social issues like abortion.

Democrats had noted that as a member of the 3rd U.S. Circuit Court of Appeals, Alito ruled on two cases involving a pair of firms that helped manage his investments -- despite a 1990 promise not to do so.

Alito said on Thursday that in filling out a questionnaire from the Judiciary Committee in 1990, "I had been unduly restrictive" in explaining how he would handle potential conflicts of interest during his "initial service."

While he had vowed to disqualify himself from cases involving certain firms, Alito wrote he later concluded "there was not a legal or ethical obligation under the applicable rules ... to recuse myself from every case involving the companies I listed."

'NO IMPROPRIETY'

Specter wrote Alito that his committee had consulted two judicial experts and he believed there was "no impropriety on your part."

But Specter added, "I believe it is important and timely for you to make a full public response on the propriety of your ruling on cases involving Vanguard and Smith Barney, Inc., at times when you had money invested in Vanguard Mutual Funds and Smith Barney, Inc., was your brokerage firm."

Wrote Specter: "In Supreme Court nominations, which are so important for so many reasons, we have seen issues which may be minor, unmeritorious, or even non-existent proliferate into major controversies."

"We hope that this will not be an issue," said Sen. Herb Kohl, a Wisconsin Democrat. "But we are pursuing it because it is our responsibility."

Sen. John Cornyn, a Texas Republican, said, "Judge Alito's letter makes clear that there is no basis for any claim of impropriety -- though I have no doubt that the critics will continue to pursue other rabbit trails."

Alito earlier told senators during private meetings that a glitch in the court's computer system was part of the problem in failing to flag a Vanguard case in 2002.

After he ruled in the case as part of a three-judge panel, his participation was challenged by a party in the case. Alito then removed himself from further consideration. He earlier participated in a case involving Smith Barney.

The White House has denied wrongdoing by Alito, saying he was under no legal obligation to recuse himself. It said while the firms did help manage his mutual funds, he had no financial stake in either or the court cases involving them.

Commentary:
The man made a promise, broke it and lied about it. What kind of man doesn't know who manages his money? A liar or a man who's so out of touch with the real world he's unfit to be a judge. If a company managed my money, you can bet your bottom dollar I'd know its name. Alito has lots of excuses - even blaming a computer problem for not alerting him to a possible conflict of interest with the company that manages his money. If he needs a computer to tell him, he's unfit.