WASHINGTON. — It is fair for Mr. Bush to say that Clarence Thomas, his nominee for the Supreme Court, is ''much closer to the mainstream of America than some of the groups that are opposing him.'' This is politics, after all. It is even fair for the president to assert, as he did in announcing his selection, that Judge Thomas is the best qualified person in the nation to sit on the high court.
It is not fair for Mr. Bush and his nominee to demand senatorial confirmation without offering some proof of those claims.
Politicians cite public opinion polls when they suit their purpose, and ignore them otherwise. Mr. Bush maintains that ''overwhelming support is now showing up for Judge Thomas in measurable ways, not only in the minority communities but across the board.'' That apparently alludes to the Gallup Poll that showed 57 percent of blacks surveyed favored the Thomas nomination.
At the same time, the NAACP, the black National Bar Association and the AFL-CIO have gone on record against it. Presumably these are the opposition groups the president deems remote from the mainstream.
Whether that 57 percent poll figure will shift when the NAACP and the black churches have had time to pass the word about Judge Thomas is yet to be seen. No one, not even Mr. Thomas or the president, is watching closer than the freshman southern Democratic senators whose narrow winning margin was provided by black voters in 1986.
They include Richard Shelby of Alabama, who won by a 50-49 percent margin; Terry Sanford of North Carolina, who won by 52-48, and Wyche Fowler of Judge Thomas's native state of Georgia, who won by 51-49. How they vote on the Thomas nomination could tip their re-election efforts next year -- and if they were forced to vote now, they would have to decide whether black interest groups or opinion polls carry more weight in their states.
The alternative, of course, is to base their decision on the philosophical merits of the nomination, rather than political arithmetic.
But if the White House succeeds in the high-pressure public jTC relations campaign it is running, the Thomas philosophy will be submerged in warm and fuzzy rhetoric about how he rose from poverty: If those motherly black ladies brought up from Georgia to visit him the other day say he's still the same nice young man he used to be, questions about his years at the Equal Employment Opportunities Commission will seem to be unnecessarily picky.
Just such tactics brought Justice David Souter through the nomination process unscathed last year. He gave vague, good-natured answers to some questions, and courteously declined to answer others because they might somehow relate to the job he was picked for. He gave the senators nothing to get their teeth into.
They were in a honeymoon mood toward a new president, and feeling generous after rejecting the 1987 nomination of Robert -- Bork, whose long paper trail and combative attitude did him in. There is a pendulum tendency in confirmations; after voting against one nominee, senators are more likely to accept the next one or two. By that pattern, Judge Thomas might expect rough handling, because both Anthony Kennedy and Justice Souter have been approved since Bork was turned down.
Mr. Thomas is now cooperating in the White House effort to smooth his way through, but he started too late. The maverick quality that charmed a president determined to pack the court with conservatives makes Mr. Thomas more of a controversial Bork than a bland Souter.
His opposition to affirmative action while at the EEOC defied the commission's original goals, as well as his own background -- he has profited repeatedly from just the kind of preferential treatment he disdained for others. That contradiction needs to be explained.
He has offered a hint to how he would think on the Supreme Court by speaking favorably of something called ''natural law.'' This is a concept given passing notice in the opening words of the Declaration of Independence, but it is not spelled out elsewhere by the Founding Fathers. Like the Constitution, it means whatever its interpreter thinks it means; the difference is that the Constitution is a written document to which every official, including Supreme Court justices, must swear obedience.
What does natural law mean to Judge Thomas? How would he apply it to interpreting the Constitution? How would it affect his thinking on affirmative action, school prayer, abortion, flag-burning?
Mr. Bush says he has never asked Mr. Thomas about such issues. He doesn't say others have not asked on his behalf. It's the Senate's turn, and duty, to demand answers for the rest of us.
Ernest B. Furgurson is associate editor of The Sun.