By Joan Biskupic

WASHINGTON (Reuters) - They are heavyweights in the ring that is the U.S. Supreme Court.

These button-down, Ivy League-credentialed versions of Muhammad Ali and Joe Frazier represent Washington versus the states and the competing left-right ideologies behind that conflict. And the punches they throw - and take - while at the courtroom lectern have captured as much attention as their stances on the law.

U.S. Solicitor General Donald Verrilli and Washington lawyer Paul Clement squared off over healthcare and immigration policy, the two biggest cases in the court term that ended in June. They are likely to do battle again over months, and perhaps years, to come.

Their rivalry arises largely from a distinct moment in U.S. legal history: Republican-controlled states have aggressively challenged the Democratic administration of President Barack Obama. Verrilli, appointed by the president, is the government's top courtroom lawyer. Clement, who was a solicitor general during the Republican administration of President George W. Bush and is now with Bancroft PLLC, has become the go-to lawyer for conservative states and other challengers of the administration.

"You have to go back a long way to find two people who are consistently representing such opposing views," said Andrew Pincus, a Washington lawyer who appears regularly before the court.

Not only are states increasingly locked in litigation with the federal government, Pincus said, but they are also going outside the offices of the states' attorneys general for Supreme Court specialists.

STUDY IN CONTRASTS

A 46-year-old Wisconsin native, Clement approaches the lectern below the justices' bench with no notes and a steady stock of rejoinders. He exudes confidence and seems to relish sparring with the nine justices, left and right.

Verrilli, 55 and a New York native, is low-key and soft-spoken. When he began as solicitor general last year, the justices sometimes had trouble hearing him. His presentations have been halting at times, and he stumbled when he began his defense of the healthcare law's insurance mandate during the March session.

Verrilli coughed as he started to speak, then choked on a gulp of water. Overall, he had a rocky time before a bench dominated by conservative justices, who pummeled him with skeptical queries. At one point when Chief Justice John Roberts told Verrilli he had an extra 15 minutes, Verrilli said with a sigh, "Lucky me. Lucky me."

News commentators lambasted Verrilli's performances in the healthcare and immigration disputes and contrasted them with Clement's fluid style. Some deemed his arguments nearly fatal for the Obama administration.

Setting the tone for much of the healthcare postmortem, CNN commentator Jeffrey Toobin proclaimed Verrilli's arguments in March "awful" and "a train wreck."

In the end, Verrilli, on behalf of the administration, prevailed as the court upheld the requirement that most Americans buy health insurance and ruled, in the immigration case from Arizona, that federal law overrides most state policy.

Only this week did Verrilli publicly comment on his performance and the media drubbing. On a panel at the Heritage Foundation in Washington, D.C., on Wednesday, he first took a lighthearted approach. As he was about to begin his panel presentation, he said, "I'm just going to take a sip of water here." The audience laughed knowingly, recalling the dry throat that got him off to a bad start during March arguments.

In response to a question later about the criticism, he said, "I'm a government official. I've got a weighty responsibility. I ought to be subject to criticism like any other official with a weighty responsibility. And I guess I was. I'm OK with that."

LEGAL SCORECARDS

Clement has 62 Supreme Court arguments under his belt, Verrilli, 21. This term, Clement argued seven cases, winning four and losing three. Verrilli split his six: three wins, three losses. Such scorecards are imperfect indicators of a lawyer's skill: For the justices, much depends on the validity of each side's core legal position and how they fit with past relevant cases.

The two advocates confront each other indirectly - through the justices, in fact. Each individually fields questions for his respective time, usually 30 minutes a side.

Outside the courtroom, things can be even tamer. Verrilli and Clement are part of a league of appellate lawyers that rarely engages in personal criticism. They are among the best-mannered of their ilk, down to their starched shirts and cuff links. At a Georgetown University law school event in March, Verrilli said he held Clement in high regard. Clement, vacationing this week, said in a brief email exchange, "I think the world of Don." Both men declined further comment for this story.

Verrilli, tall with a salt-and-pepper mustache, and Clement, medium height with thinning brown hair, climbed the elite ranks of the law in similar fashion. But once they set on a professional path, they diverged in political and ideological affiliations.

Verrilli, who attended Yale University and then Columbia University law school, was a law clerk to jurists known for their liberalism: Supreme Court Justice William Brennan and, earlier, U.S. Appeals Court Judge Skelly Wright of the District of Columbia Circuit.

Clement attended Georgetown University and Harvard Law School. His mentors were leading lights of conservatism: Supreme Court Justice Antonin Scalia and, earlier, U.S. Appeals Court Judge Laurence Silberman of the District of Columbia Circuit.

Clement became principal deputy to U.S. Solicitor General Theodore Olson in 2001, then gained the top SG job in 2005, a year short of age 40. Continued...