WASHINGTON – While President Bush’s nomination of Judge John Roberts Jr. to the Supreme Court drew little outright opposition from Democrats, a battle quickly took shape over some senators’ demands that the nominee make clear his views on a host of issues, from abortion to the environment.

Announcing the selection of Judge Roberts last night, Mr. Bush praised the judge’s insight and his character. “John Roberts has devoted his entire professional life to the cause of justice and is widely admired for his intellect, his sound judgment, and personal decency,” the president said. “I have been deeply impressed. He’s a man of extraordinary accomplishment and ability. He has a good heart.”

Mr. Bush also signaled he is confident that Judge Roberts, a Buffalo native whose judicial experience is limited to just two years on the D.C. Circuit appeals court, will adhere to conservative judicial precepts. “He will strictly apply the Constitution and laws, not legislate from the bench,” the president said.

Beneath the glaring television lights in the White House’s formal East Room last night, Judge Roberts, 50, looked a bit ill at ease. He said he was honored and humbled by the nomination. “Before I became a judge, my law practice consisted largely of arguing cases before the court,” the judge said. “I always got a lump in my throat whenever I walked up those marble steps to argue a case before the court, and I don’t think it was just from the nerves.” He offered tributes to his family before promising to “work to preserve the institutions of our democracy.”

On Capitol Hill, Democratic senators who had been set to come out swinging against some potential nominees reacted with caution to Judge Roberts. The ranking Democrat on the Judiciary Committee, Senator Leahy of Vermont, spoke in generalities about the Senate’s obligations to carefully examine Mr. Bush’s choice.

“To fulfill our constitutional duties, we need to consider this nomination as thoroughly and carefully as the American people deserve,” Mr. Leahy said. “No one is entitled to a free pass to a lifetime appointment to the Supreme Court. Someone confirmed today can be expected to serve on the court until the year 2030 or later.”

Another Judiciary Committee member, Senator Schumer, offered some praise for the nominee, along with a warning. “There is no question that Judge Roberts has outstanding legal credentials and an appropriate legal temperament and demeanor, but his actual judicial record is limited to only two years,” Mr. Schumer said. “Many of his personal views are unknown. … It is vital that Judge Roberts answer a wide range of questions openly, honestly, and fully in the coming months.”

Mr. Schumer noted that he voted against Judge Roberts’s nomination to the appeals court post because of the judge’s refusal to answer a question seeking the names of three Supreme Court decisions with which he disagreed. The senator said such evasion would not be tolerated this time. “Now, it’s a whole new ball game,” Mr. Schumer said.

One of the most wary reactions came from a former Democratic presidential nominee, Senator Kerry of Massachusetts. He said Mr. Bush’s nominee is a far cry from the judge he would replace, Justice O’Connor. “Judge Roberts is no Sandra Day O’Connor, and the White House has sent a clear signal,” Mr. Kerry said. The senator called for questioning of Mr. Roberts that would expose his views on civil rights and the landmark abortion decision, Roe v. Wade. “These issues are in serious question if you take even a cursory glance at his record,” Mr. Kerry said.

Senator Clinton issued a statement that expressed no opinion on the nomination but called for a “thorough examination” of Judge Roberts’s rulings and legal career. While most Democratic senators kept their powder dry, liberal interest groups expressed disappointment in the president’s selection. Abortion rights advocates voiced some of the loudest criticism. “We are extremely disappointed that President Bush has chosen such a divisive nominee,” the National Abortion Rights Action League said in a statement.

Some of the group’s concern may stem from a brief Mr. Roberts signed as deputy solicitor general in the Reagan administration. The legal pleading argued that Roe v. Wade was wrongly decided. Backers of Mr. Roberts contend that his signature offers no indication of his personal or even professional views on abortion. “It was his job to sign the brief,” a Supreme Court litigator, Thomas Goldstein, told The New York Sun earlier this year.

The chairman of the Judiciary Committee, Senator Specter of Pennsylvania, said he was “concerned” about the early attacks on Judge Roberts by abortion rights groups. “At a minimum, people ought to give him an opportunity to be heard,” Mr. Specter said.

Other Republican senators also offered quick support for Judge Roberts, as did conservative activists. Senator Hatch of Utah said the nation would not allow Democratic senators to abuse the nominee. “I don’t think the American people are going to put up with any more crap from the Judiciary Committee,” Mr. Hatch told Fox News.

A former Justice Department attorney who now works at the Heritage Foundation, Paul Rosenzweig, called Judge Roberts “a fantastic choice.”

“He’s clearly one of the top lawyers in America in terms of ability,” Mr. Rosenzweig said. “He doesn’t have a huge track record, so it’s hard to be 100% sure, but everything I know about him suggests he’s very much going to be more in the Scalia, Thomas mold than would be lots of other possibilities.”

Mr. Rosenzweig said that as the debate about Mr. Roberts begins, Democrats may fret about his intellect, which could help conservatives win close cases before the Supreme Court. “It may very well turn out to be a big battle, because I think the Democrats may be very afraid of a very, very smart conservative man.”

While some clash over the nominee appears certain, the only mechanism Democrats could use to block the nomination would be the filibuster. A key player in brokering an agreement limiting use of the tactic, Senator Lieberman, a Democrat of Connecticut, told reporters last week that Judge Roberts would not prompt a filibuster, according to the Hartford Courant.

Judge Roberts’s slender record at the appeals court contains a few decisions that augur well for conservatives and are likely to draw fire from at least some Senate Democrats. Just last week, he joined a D.C. Circuit ruling upholding the administration’s right to proceed with military trials for war-on-terror prisoners held at Guantanamo Bay.

In 2003, Judge Roberts filed a dissent that indicated he has questions about the scope of Congress’s authority in passing laws like the endangered species act. He argued that the federal government’s efforts to protect a particular species of toad may have gone too far because the species is found only in California, and the dispute could not be said to have had any impact on interstate commerce.

In another decision that critics may paint as hard-hearted, Judge Roberts last year ruled that the arrest and handcuffing of a 12-year-old girl in a Washington subway station involved no constitutional violation. The girl’s alleged misdeed: defying the transit system’s rules by consuming a single french fry.

Judge Roberts graduated from Harvard College in 1976 and Harvard Law School in 1979. There is some indication that his experiences there during the Vietnam era helped to shape his conservative outlook. Leftist students protesting in favor of Communist leader Ho Chi Minh “did not sit well” with Mr. Roberts, the newspaper Legal Times reported earlier this year.

After law school, the future judge went on to work for two conservative icons. He served as a law clerk for Justice Rehnquist and as an associate White House counsel for President Reagan. Mr. Bush pointed out both those connections as he introduced the nominee to the nation last night.