WASHINGTON — Senators from both parties said yesterday they plan to question whether White House adviser Karl Rove may have given inappropriate "back-room assurances" to secure conservative support for Supreme Court nominee Harriet Miers.

Sen. Arlen Specter, R-Pa., chairman of the Senate Judiciary Committee, said his committee "is entitled to know whatever the White House knew" regarding Miers and her views on important legal issues.

"If there are back-room assurances, and if there are back-room deals, and if there is something which bears upon a precondition as to how a nominee is going to vote, I think that's a matter that ought to be known by the Judiciary Committee and the American people," Specter said on ABC's "This Week."

Sen. Patrick Leahy of Vermont, the ranking Democrat on the committee, said he would oppose any nominee who gives assurances about how he or she would vote on particular cases.

"I would vote against that person," he said. "I wouldn't care whether they are nominated by a Democrat or a Republican ... and all 100 senators should vote against them under that basis alone."

Leahy said Miers has told him that she has given no such assurances.

The White House acknowledged Rove has been among those making calls to key conservative supporters but denied anything improper has been promised.

The issue arose from remarks made on a syndicated radio show by James Dobson, founder of the conservative advocacy group Focus on the Family. Dobson said last week that he had spoken in confidence with Rove about the Miers nomination and that their conversation convinced him to support her.

"When you know some of the things that I know, that I probably shouldn't know, you will understand why I have said ... that I believe Harriet Miers will be a good justice," Dobson said.

Dobson was unavailable for comment yesterday.

His remarks have triggered concern in both parties that Miers has revealed how she might vote, if confirmed, on sensitive issues such as abortion, school prayer and gay marriage. Even if she hasn't, critics suspect the president has private knowledge regarding Miers' views that he is not sharing with those who must vote on her confirmation.

Both Leahy and Specter said they would be willing, if necessary, to summon Dobson and Rove to clear up the matter. However, it is doubtful that Rove would agree to testify before the committee, since as a presidential adviser he is subject to a White House assertion of executive privilege.

Some conservatives have continued to express concern that Miers, President Bush's White House counsel and formerly his personal lawyer in Texas, lacks the credentials to replace a pivotal Supreme Court moderate, Sandra Day O'Connor. Implacable abortion foes such as Sen. Sam Brownback, R-Kan., say they are dissatisfied with White House guarantees that as an evangelical Christian she opposes abortion.

"A lot of us wanted to see somebody that was a well-formed jurist so that they had a track record of what they would do in cases coming in front of the court," Brownback said on CBS News' "Face The Nation." "Harriet Miers doesn't have that track record and doesn't seem to be well-formed in her judicial philosophy, having never been on the bench."

Nathan Hecht, a Texas Supreme Court justice and a longtime friend of Miers who has been speaking out on her behalf over the last week with the support of the White House, said that although Miers had long opposed abortion she would set aside her personal views when deciding cases.

"Legal issues and personal issues are just two different things," Hecht said on "Fox News Sunday."

But Gary Bauer, head of the conservative advocacy group American Values Coalition, said on the same program that conservatives would be disappointed if that were the case. "If he wants to reassure his fellow pro-life conservatives, that's the last argument he should be making," Bauer said.

"You can be an evangelical and you can be self-described pro-life. But it doesn't tell us what she will do about a decision like Roe [v. Wade, which legalized abortion] that has been set in stone now for over 30 years. And that's the rub," Bauer said.

Specter cautioned against a rush to judgment on Miers, saying her critics have put together "one of the toughest lynch mobs ever." But Miers will need to be able to justify to senators whether she is qualified in order to be confirmed, he said.

"When you deal in constitutional law, you're dealing in some very esoteric, complicated subjects that require a great deal of background," Specter said. "The jurisprudence is very complicated, and I will be pressing her very hard on these issues."

Specter and Leahy said they will strive to hold confirmation hearings as soon as possible, perhaps before Thanksgiving, but their primary concern was to conduct a thorough investigation. "The standard is to do it right, not to do it fast," Specter said.

Compiled from reports by The Dallas Morning News, the Los Angeles Times, The Washington Post and The Associated Press