Senate Democrats are pressing Supreme Court nominee Samuel A. Alito Jr. about his rulings on cases that involved financial companies in which he had investments, a sign that ethics questions may play a role in his confirmation hearing.

In letters and private meetings this week, several Democratic senators asked Alito for fuller explanations of why he ruled, as a federal appellate judge, on cases regarding Vanguard and Smith Barney Inc. after promising to recuse himself from those cases. Alito had at least $390,000 in Vanguard mutual funds when he ruled in a 2002 case that favored the company. He also ruled in a 1996 case involving Smith Barney, which was his brokerage firm.

Alito has said that a court computer system failed to remind him to step aside in the Vanguard case. And the White House has argued that the court rulings could not have affected his personal finances in any meaningful way. Democrats concede that point, but say they are troubled that the nominee failed to withdraw from the cases, as he had said he would, to avoid any possible conflict of interest.

The Senate Judiciary Committee's eight Democrats yesterday sent a letter to the chief judge of the Court of Appeals for the 3rd Circuit, where Alito sits, asking for details of the Vanguard case. The request includes "any communication from or to the White House, the Justice Department (including the FBI), or Judge Alito, or anyone else on their behalf, in respect to the reasons why Judge Alito failed to recuse himself, . . . including the recent White House statement regarding a computer failure."

On Tuesday, the committee's most senior member, Edward M. Kennedy (D-Mass.), wrote to Alito asking for an explanation. A background paper issued by Kennedy noted that "ethical issues" helped derail Abe Fortas's bid to become chief justice in 1968 and Clement Haynsworth's 1969 nomination to be an associate justice.

Two Senate Democrats who met with Alito yesterday said they were not fully satisfied with his explanation of the Vanguard matter. Addressing reporters, Sen. Kent Conrad (D-N.D.) said he told Alito he was troubled by the case, and Alito's "response was he just didn't focus on it, that it was a very minor amount [of money involved], that the issue with Vanguard would have no effect at all on his holdings, which is clearly true."

Conrad said he told Alito, "You are ultimately the check on whether or not you kept your pledge. You indicated you would recuse yourself, and then did not." On balance, Conrad said, he was very impressed with Alito. "He got off to a very good start with me," Conrad said.

Sen. Charles E. Schumer (D-N.Y.) said Alito told him about the court's computer glitch, "but there are a few things you have to check out. A part of it relates to how the 3rd Circuit works in terms of telling people when to recuse themselves."

Alito's backers say Democrats are focusing on the recusal question because they are having little success challenging his qualifications or judicial philosophy. Some law professors have written the Judiciary Committee defending his role in the Vanguard case. "In my opinion Judge Alito handled it quite properly, in correcting a situation in which he can be said to have made a mistake about recusal," wrote University of Pennsylvania law professor Geoffrey C. Hazard Jr.

When the Judiciary Committee confirmed Alito to the appellate court in 1990, he promised in writing to disqualify himself from any cases involving Vanguard or Smith Barney. But in 2002, he and two other judges ruled in Vanguard's favor by dismissing a complaint that the company had improperly seized some private accounts and blocked the owner's widow from obtaining the money in them. When the woman complained, the court set aside the judgment and had another panel of judges hear the case.