For a whole range of reasons, the con- firmation hearings on Harriet Miers, President Bush's choice for the Supreme Court, have become a supreme test for the president himself. The timing, the circumstances and the substance of the hearings all magnify the importance of the outcome.

In some respects, this heightened political gamble by Miers was preordained when Bush decided to select a member of his inner circle of White House advisers as Justice Sandra Day O'Connor's successor. Earlier this fall, he could bask in the reflected glory of Judge John Roberts, named to the vacancy created by the death of Chief Justice William Rehnquist.

Roberts was no presidential pal, but his credentials were obvious and recognition of his superior talent commended Bush's good judgment.

By contrast, Miers was largely unknown in larger legal and political circles. Her sole credential was the personal confidence she had earned from Bush as his private attorney, as an official in his Texas administration and as White House counsel.

The surprise when he picked her -- rather than one of the distinguished federal appeals court judges conservatives had expected -- clearly extended to the White House political staff. Her introduction to the public was as badly bungled as anything since Bush's father shocked his staff by choosing Dan Quayle as his running mate.

The usually smooth White House "spin machine" stuttered at the outset, unsure of what to claim on her behalf, and Miers was nearly mute in making the case for herself. Meantime, angry conservatives of all stripes vented their frustration by publicly questioning her credentials.

The rift on the right silenced some of the president's normally reliable advocates in the Senate. While fellow Texans rallied to support the Dallas lawyer, hesitancy among other Republicans impelled the president and first lady Laura Bush to speak out in defense of the nomination.

The effect was to raise their personal stakes in the Miers choice even higher. Her rejection, they implied, would not challenge merely her own qualifications but the Bushes' judgment about her worth.

Thus, with one fateful choice, the president both heightened the political bet he made and managed, for the first time, to open a major breach within his coalition of supporters. In a misguided effort to reassure them, her backers then touted her adult conversion to a fundamentalist faith -- implying that the religious right should take comfort. The criticism of the tactic caused the White House to reverse course.

Meantime, Miers sowed confusion about her abortion stance. When longtime Texas friends identified her as a right-to-lifer, she vowed that no one knew her views on that issue. The next day she revealed that on a 1989 questionnaire from an antiabortion group she had promised to support a broad constitutional amendment to ban abortion.

The problems were compounded by Miers's travails in her early dealings with the Senate. The courtesy calls she made on members of the Judiciary Committee left many of them with more questions than answers. Particularly unsettling was her session with Arlen Specter, the Pennsylvania Republican who heads the committee. After a long meeting with her, Specter told reporters that Miers had told him she supported the Griswold decision, which enunciated a constitutional right to privacy. That decision became a precedent for later abortion rights rulings.

Hours later, Miers phoned Specter and asked him to correct his statement, saying she had not endorsed Griswold. The senator acceded to her request, but told reporters that his recollection of their meeting had not changed and that he would revisit the question during the hearings, with cameras present, so there could be no misunderstanding.

It was not the way a witness wants to launch her relationship with the senator presiding at her hearing.

The examination of Miers will come at a difficult time for Bush. In early November, his job approval polls, which have been touching new lows almost every week, are likely to be further damaged by the arrival of the first high home heating bills of the winter. Iraq, even after the constitutional referendum, remains an unhealed wound. The off-year elections in New Jersey and Virginia could prove troublesome for Republicans. He badly needs to catch a break, and instead he will be offering up to the Senate Democrats -- and some restive Republicans -- a nominee who looks vulnerable.

It is only fair to say, as Sen. Lindsey Graham of South Carolina has argued, that Miers deserves the opportunity to make the case for herself. The condemnation of her from some on the right seems over-hasty and picayune.

But the burden of proof is on her shoulders -- and much of Bush's own credibility is right there with it.

davidbroder@washpost.com