Under pressure, some people talk a bit faster, some talk a bit louder, some get tongue-tied or sound irritated. Supreme Court nominee John G. Roberts Jr.'s voice changes not one whit.

His genial tone comes through on tapes of his many oral arguments as a lawyer before the high court. Here, years of litigation and months of preparation come down to 30 minutes of mental jujitsu with a constantly interrupting panel of contentious justices. But Roberts greets every snappish interjection, every odd hypothetical question, every hostile digression with the same unhurried yet purposeful voice.

This unflappability will be tested again starting Sept. 6, when Roberts goes before the Senate Judiciary Committee for a multiday confirmation hearing. The session is sure to feature hostile questions from Democratic senators worried about the nominee's views on civil rights, abortion, judicial ethics and the role of courts. His testimony before the same committee two years ago, when he was appointed to the federal bench -- and his years as one of America's most effective appellate advocates -- suggests that Roberts will be ready for that test.

Roberts sailed through his earlier hearings, even as the tone of the questions got pretty hot. Here's Sen. Charles E. Schumer (D-N.Y.), for example, scolding Roberts for dodging questions about judicial philosophy:

"You are making this an absurd process, sir, when you are saying that you can't answer even broad questions about specific jurisprudence, when you can't say how you feel about previous court cases."

The response was typical Roberts: cheerful, outwardly humble, yet giving up nothing. "I'm not sure that I could give an intelligent answer," the witness answered, "because I do think the philosophies of the justices are pretty hard to pin down. . . . To go back and analyze all of the cases and see, was this justice adopting this philosophy in this case, or this one that philosophy in another case -- I guess I just didn't feel capable of doing that."

Colleagues say the key to Roberts's poise under pressure is the immense preparation he gives to his cases. He once told David Frederick, a fellow lawyer, that he spends at least five weeks preparing for a 30-minute argument.

"The secret is developing a method for taking the hostile question that you didn't want to answer and transforming it into an affirmative point that advances your client's cause," Frederick explained in a recent interview. "Judge Roberts is one of the very best at that."

Then there's the voice -- an even, midwestern tenor vaguely reminiscent of the actor and film director Ron Howard. Neither stentorian nor insistent, it manages to be pleasant without being memorable, forceful without being strident. Roberts manages to sound as if he is agreeing even as he slips in a knife.

In recent weeks, Roberts has been practicing for his hearings with a team of advisers, trying to anticipate the questions he will face and best ways to answer them. But you might say he has been getting ready for much of his adult life. One of his first jobs as a Justice Department aide in the early 1980s was to help coach Sandra Day O'Connor -- whose seat he is now seeking to fill -- through her confirmation testimony. He advised O'Connor to keep her answers general and to avoid specifics.

This was his strategy two years ago. He presented himself to the Judiciary Committee as a sort of judicial Everyman, an unbiased arbiter who takes cases one by one with only the law and the relevant facts to guide him. Such a judge demurs when asked about issues in advance and declines to criticize the work of others. The senators wore their politics on their sleeves, but Roberts was bland as he answered -- or sidestepped -- their questions.

"My practice has not been ideological in any sense. My clients and their positions are liberal and conservative across the board," he said. "I have argued in favor of environmental restrictions and against takings claims. I've argued in favor of affirmative action. I've argued in favor of prisoners' rights under the Eighth Amendment. I've argued in favor of antitrust enforcement. At the same time, I've represented defendants charged with antitrust cases."

Patiently pretending that every question was sincere and thought-provoking, betraying neither irritation nor disdain, Roberts turned his answers into recitations of his favorite arguments.

For example:

Sen. Richard J. Durbin (D-Ill.) accused Roberts of employing "dance steps" to avoid describing his views on such topics as whether there is a constitutional right to have an abortion. "What is your position on Roe v. Wade?" the senator asked.

Roberts answered mildly. "Roe v. Wade is the settled law of the land. . . . It's a little more than settled. It was reaffirmed in the face of a challenge. . . . There's nothing in my personal views that would prevent me from fully and faithfully applying that precedent."

The answer neatly captured the proper deference that a lower court judge should give to Supreme Court precedents. But it did not exactly go to the question on Durbin's mind.

At another point, Sen. Russell Feingold (D-Wis.) tried to pin Roberts down on the death penalty.

"I think one thing that is unfair about the system is that it is not . . . certain, it's not definite, and there doesn't seem to be any reasonable time limitation," Roberts answered. "The effectiveness, if you believe in capital punishment, the effectiveness of capital punishment diminishes if the crime was committed 30 years ago. And if it takes that long to get through the system, it's not working, whether you're in favor of the death penalty or opposed to it."

The answer had something for everyone: For opponents of capital punishment, there was the framing idea -- that there is something "unfair" about the death penalty. But for supporters, he offered the view that appeals must be accelerated. His final note tried to gather up all sides -- whether "in favor of the death penalty or opposed."

All the answer lacked was an expression of Roberts's personal views.

This approach irritated some Democratic committee members who believed that Roberts might hold stronger beliefs than he was letting on, and they insist that he must be more forthcoming this time around. When the nominee paid a courtesy call to Durbin shortly after his nomination, the senator put Roberts on notice: "I said, 'If you will be more open and honest with your answers to us, it will go a long way,' " Durbin recounted in an interview.

Democrats are preparing for a far more extensive examination this time around. They have demanded more paperwork, hoping to find expressions of Roberts's political opinions. They have announced, from the moment he was nominated, that they expect him to answer questions about judicial philosophy.

"What we need to do is ask the obvious questions," Durbin said. "The country is closely divided and the court is closely divided, and we need to be sure that this institution is in the mainstream of American thinking."

But just as he did in 2003, Roberts probably will try to fend off such questions by citing the circumspect testimony of a Democratic nominee to the court, Ruth Bader Ginsburg. During her 1993 confirmation hearing, Ginsburg refused to go into the details of controversies that might come before the court.

"The reason that she thought it was inappropriate to answer that question is because it is an effort to obtain a forecast or a hint about how a judge will rule on a particular case," Roberts said in a typical response during his 2003 testimony.

So Roberts may be a bad bet for fireworks -- but the committee can often be counted on for vivid moments. No panel in Congress can match the Senate Judiciary Committee's recent record for partisanship, finger-pointing and road-blocking, not to mention computer espionage and hearing-room vulgarity. The 2003 grilling of Roberts ended with then-Chairman Sen. Orrin G. Hatch (R-Utah) chastising Schumer for asking "dumb-ass questions."

Roberts just listened quietly, unflappably -- and was confirmed soon afterward by a unanimous Senate.

John G. Roberts Jr., known for his preparation, has advisers helping him practice for the Sept. 6 start of the confirmation hearing.