WASHINGTON -- In a letter yesterday to Judge John G. Roberts Jr., Senate Judiciary Committee Chairman Arlen Specter said he plans to probe the Supreme Court nominee's interpretation of Congress' power to regulate interstate commerce, which has underpinned many civil rights, worker protection and environmental laws.

The high court in recent years has scaled back that power by narrow conservative majorities.

The Pennsylvania Republican said in the letter that he sees "a great deal of popular and congressional dissatisfaction with the judicial activism" that trimmed congressional authority under the Commerce Clause. Specter characterized lawmakers as "irate about the court's denigrating and, really, disrespectful statements about Congress' competence" in several recent cases.

Specter focused on two decisions: the 1995 ruling in U.S. v. Lopez that said Congress lacked authority to make it a federal offense to possess a firearm in a school zone, and the 2000 decision in U.S. v. Morrison that overturned a provision of the Violence Against Women Act that had allowed women who had been attacked to sue assailants in federal court. In both cases, a majority of the justices said Congress was intruding on state prerogatives and overstepping its constitutional authority.

In the Morrison case, Specter wrote to Roberts that Chief Justice William H. Rehnquist, writing for the majority, had questioned Congress' "method of reasoning." Specter continued: "To this senator, who has labored through 25 years of intense legislative hearings and fact-finding, plus prior public service and experience in the real world, my immediate reaction is to wonder how the court can possibly assert its superiority in its 'method of reasoning' over the reasoning of the Congress."

At the confirmation hearings that begin Sept. 6, Specter advised that he'll ask Roberts whether he believes that the court has more competence than Congress to decide the reach of the Commerce Clause. He'll also be asked to explain his thinking about how the high court decided U.S. v. Lopez and U.S. v. Morrison, rulings that Specter described as essentially overturning "almost 60 years of Congress' power under the Commerce Clause."

In a thinly veiled warning, he wrote of what he sees as "the Senate's determination to confirm new justices who will respect Congress' constitutional role."

The concerns Specter expressed yesterday dovetailed closely with those raised by key committee Democrats and again highlighted the chairman's role as a possible swing or tie vote for confirmation. The Judiciary panel has 10 Republicans and eight Democrats.

Many conservatives favor the Rehnquist court's narrow view of congressional power under the Commerce Clause and believe that many federal social programs, rights and regulations that rely on it for legal legitimacy have usurped powers rightly held by the states.

Liberals have tended to view the Rehnquist court's interpretation of it as the beginning of an effort to negate a broad range of laws passed since the New Deal that encompass issues from environmental protection to civil rights, including the 1964 Civil Rights Act.

Judiciary Committee Democrats -- including Vermont's Patrick Leahy, Massachusetts' Edward M. Kennedy, New York's Charles E. Schumer and California's Dianne Feinstein -- all have said Roberts' perspective on the Commerce Clause could be pivotal in their deliberations on his confirmation -- as well as his views on privacy rights and the 1973 Roe v. Wade decision that legalized abortion.

Leahy recently told reporters that the current Supreme Court is "the most activist" in his lifetime "in striking down congressional enactments, whether in environmental laws or the Violence Against Women Act, child safety." He said he wanted to know the nominee's views on whether "we are reaching the point where the Commerce Clause is totally gutted."

Democrats have emphasized their concerns about a 2003 dissent written by Roberts, a judge on the U.S. Court of Appeals for the D.C. Circuit, in a case known as Rancho Viejo LLC v. [Interior Secretary Gale A.] Norton.

Roberts wanted the full court to review a decision by a three-judge panel of the court that said the federal power to protect California's arroyo toad under the federal Endangered Species Act trumped state authority to regulate land development. In making his argument, Roberts questioned whether federal authority under the Commerce Clause applied, since the toad lives only in California.

Seth Rosenthal, legal director for the liberal group Alliance for Justice, said Specter's letter to Roberts was noteworthy because the queries "were coming from a Republican senator as opposed to a Democratic senator.

"Constitutional law scholars -- conservative, liberal, middle of the road -- all of them have recognized ... the court's conservative judicial activism, in terms of striking down acts of Congress, as being sort of the hallmark of the Rehnquist court," Rosenthal said. "And conservatives generally don't talk about it because they're supportive of this kind of activism."

Schumer, who opposed Roberts' appeals court confirmation two years ago and who has already given the nominee an expansive list of questions he plans to pose at next month's hearings, saw Specter's letter yesterday as an opening to drill into details of Roberts' views on the Commerce Clause and other aspects of his judicial philosophy.

"Arlen Specter sounds exactly like Chuck Schumer, and his letter is just what the doctor ordered," Schumer said in a statement. "Judge Roberts should understand that answering specific questions to vital issues is an obligation, not an option, for anyone who aspires to the Supreme Court. Senator Specter's questions aren't exactly identical or as numerous as the 80-plus that I've asked of Judge Roberts, but the spirit of asking them and the need for a response is the same."

But Walter E. Dellinger III, who served as acting solicitor general from 1996 to 1997 and who teaches constitutional law at Duke University Law School, said Specter's questions "by no means suggests that Chairman Specter is taking an anti-Roberts stance.

"He, more than any senator with whom I have spoken, has been very concerned about the lack of deference shown to Congress," Dellinger said. "For at least the past 10 years, Senator Specter has believed that the court has been too quick to second-guess the legislative judgments of Congress. So it's not surprising that he would want a nominee for the Supreme Court to reflect upon these issues."