WASHINGTON - Amid intense scrutiny into the judicial record of Supreme Court nominee John G. Roberts Jr., perhaps nothing seems as curious as the hubbub surrounding his brief remarks two years ago about a striped toad in California.

The judge's four-paragraph argument that the endangered toad should not be protected by federal environmental laws strikes at the heart of many rights that Americans enjoy, including such basics as a minimum wage and clean drinking water. And it will become a focal point for tough questioning during Roberts' confirmation hearing next month, the chairman of the Senate Judiciary Committee said yesterday.

"This is much bigger than abortion or affirmative action," said Roger Pilon, a court watcher at the Cato Institute, a libertarian think tank. "It's the main issue: How much power did we give the federal government?"

At issue is the Constitution's commerce clause, which, the court has determined, gives the federal government broad regulatory powers.

Roberts' government writings have raised questions about whether he might seek, under the clause, to narrow federal laws on issues involving equal opportunities for women to play college sports and voting rights for minorities.

In the case of the arroyo toad, Roberts argued that because the toad was found only in one state, interstate commerce was not affected and the toad should not qualify for federal protection under the clause.

Such a view, if applied widely, could undermine a range of protections established by Congress. Roberts' writings have raised questions about whether he would seek to narrow use of the clause to scale back laws giving women equal opportunity to play college sports and minorities the right to vote freely.

Thus it is no small matter to liberals and conservatives concerned about how Roberts would interpret the clause.

"People are really concerned," said Neil Richards, a Washington University law professor who, like Roberts, was a Supreme Court clerk for William H. Rehnquist.

"The civil rights laws," Richards said, "have a relatively tenuous link to interstate commerce. If the court says the commerce clause only regulates commerce, then what does that mean for civil rights laws? It starts to look scary."

At least one member of the Senate Judiciary Committee, Sen. Charles E. Schumer of New York, a Democrat, has asked Roberts for his views on the clause, his spokesman said. Two other committee members, Republican Arlen Specter of Pennsylvania and Democrat Edward M. Kennedy of Massachusetts, say they will ask for Roberts' views during confirmation hearings.

Yesterday, Specter, chairman of the committee, sent Roberts a letter saying members of Congress were "irate" that the Supreme Court had in recent years rejected some federal laws citing the commerce clause. He said he intends to ask Roberts for his view on the matter.

"It's going to be an appropriate area" for questioning, Kennedy said recently. The commerce clause carries "enormous importance to everyday life," he said.

Roberts has been a federal judge since 2003. Democrats in Congress haven't opposed his selection to replace retiring Justice Sandra Day O'Connor but have raised concerns, including Roberts' willingness to answer questions, access to his writings and, lately, his views on civil rights.

Democratic senators have asked the White House for memos that Roberts wrote about civil rights and certain other cases while he was deputy solicitor general under the first President Bush.

"Is Judge Roberts going to be part of the sense of progress that we've made or will he be someone that wants us to move back?" Kennedy asked. "That, I think, is the real key issue. Basically, whose side is he going to be on?"

Because it underlies some civil rights legislation, a reinterpretation of the commerce clause would be a part of any effort to curtail the laws' scope.

Conservatives have argued that courts have interpreted the clause too broadly, allowing Congress to pass laws that don't affect commerce, let alone involve activity crossing state lines. They also have attacked related "federalism" provisions that have been cited to allow health and safety regulations.

Effort to curb powers