As a close friend and political ally of President Bush, Sen. Bill Frist seemed the White House's ideal choice when he captured the Senate majority leader post in December. Yet 100 days into the job, the Tennessee Republican has stumbled in pushing the president's agenda and infuriated some fellow Republicans by cutting a last-minute deal to slash Bush's prized tax cut package.

Frist, who won his job with Bush's help, has surprised friends and foes alike with a rocky and sometimes awkward transition to power. After Republicans bragged that they needed just one more vote to approve Bush's bid to drill for oil in an Alaskan wildlife refuge, Frist's leadership team didn't find it. After Frist quietly reached out to California Democrats to strike a deal on Bush's plan to limit medical malpractice jury awards, negotiations collapsed and he had to lay the matter aside.

Even some GOP victories under Frist have come at a steep price. Senate Republicans passed tax cuts for charitable giving, for instance, but only after jettisoning much of Bush's ballyhooed faith-based initiative. Nothing, however, raised more questions about Frist than last week's tax cut negotiations, which left House GOP leaders fuming and accusing the Senate leader of purposely misleading them.

Bush pushed Frist for the job because White House officials saw him as a bridge-builder and a reliable conservative ally in the wildly unpredictable Senate. But Frist's lack of leadership experience and his apparent unwillingness to twist arms to win solid GOP backing for the president's priorities are presenting unexpected problems for Bush and the new majority leader. Frist's allies chalk up the setbacks to his unfamiliarity with running the Senate and the inherent difficulty of passing any legislation with a two-vote majority.

But several senators said Frist appears hesitant and unsure of how to push his party's most liberal members to back a conservative Bush agenda.

Frist, who is traveling in China and other Asian nations, did not respond to requests for a phone interview this week. But Eric Ueland, his senior aide, defended the majority leader's record. "We came back into a majority of a Senate that was broken," he said, and "his highest priority was to get the Senate working again. . . . With a narrow majority, we've pumped out an aggressive amount of legislation, begun to address the backlog of judicial nominees and set up the framework for major pieces of the bicameral agenda, including growing the economy, providing prescription drug coverage for seniors, an orderly appropriations process and supporting the war on terrorism and our troops in the field."

When Congress reconvenes April 28, however, Frist's first order of business may involve quelling intraparty resentment over last week's agreement to cut Bush's tax cut in half without alerting other GOP leaders in the House and Senate. His problems began when it became clear that the Senate would not pass a $2.2 trillion budget plan for 2004 that accommodated most of Bush's request for a 10-year, $726 billion tax cut. Without a budget, prospects for any tax cuts would be dim.

Two key GOP senators -- Olympia J. Snowe of Maine and George V. Voinovich of Ohio -- said they would provide the crucial votes for the budget plan only if Senate leaders publicly vowed to accept a tax cut no bigger than $350 billion. In a small huddle last Thursday night, Frist agreed to the deal.

A bit later, the GOP-controlled House -- unaware of Frist's pledge -- reluctantly agreed to a compromise that would allow a $550 billion tax cut, although it delayed the detailed decision by weeks or months. The next morning, however, Speaker J. Dennis Hastert (R-Ill.) and other House and Senate GOP leaders learned of Frist's promise to Snowe and Voinovich, and reacted angrily.

Late that night, Frist issued a statement saying that on Thursday he had been "made aware of information that I should have immediately passed on to the House leadership." The next morning he flew to China.

Sen. Lindsey O. Graham (R-S.C.), while defending Frist's leadership, warned that such deals can cause serious problems. "The way to lose everyone over time is have people feel you are not dealing straight up," said Graham, a former House member. "We've done some significant things . . . [but] all that can come to an end if people feel that trust doesn't exist." While Frist maintains strong support among Senate Republicans, Graham pointedly warned, "This can either be a bump in the road or a turn in the wrong direction."

In a sign of possible tension among GOP leaders, Rick Santorum (Pa.), chairman of the Senate Republican Conference, said Frist has some fences to mend when he returns from Asia. "I think it is pretty clear, yes, [House Republicans] are upset," he said.

Santorum said he was kept "out of the loop" on the tax deal, and appeared somewhat irritated. "All I can do is make the best out of this I possibly can," he said. A week earlier, he had been seen in a Senate hall emotionally urging Budget Committee Chairman Don Nickles (R-Okla.) not to yield to moderates' demands for a smaller tax cut.

Frist's biggest problems are with House leaders, with whom he eventually must strike final deals on everything from the federal budget to providing assistance to vaccine makers, a pet project of his. After last week's dust-up, House Majority Leader Tom DeLay (R-Tex.) warned of "serious long-term consequences" for Frist, and pointedly offered some advice about leadership. Some House GOP leaders privately questioned whether Frist's word could be trusted in future negotiations.

Frist is "very regretful about what transpired" with the tax deal and is determined to help heal any wounds, Ueland said. "He wants to make sure the legitimate level of frustration doesn't thwart the agenda."

Graham and perhaps some other GOP senators now plan to vote against a $350 billion tax cut later this year, further complicating Frist's job. "I want a tax cut with significant economic impact or none at all," Graham said.

Life at the top wasn't supposed to be this difficult for Frist. A rising GOP star, he was hand-picked for the job by Bush and White House political guru Karl Rove after Sen. Trent Lott (R-Miss.) was forced to resign as party leader in December. Frist's GOP colleagues elected him, without opposition, in a telephone conference call.

Frist, a heart transplant surgeon before running for office in 1994, was expected to fight vigorously for the White House's agenda. Few Republicans expected him -- or anyone, for that matter -- to easily ram Bush's priorities through the Senate, where Republicans hold a 51-49 majority in a chamber that requires 60 votes to stop filibusters. But the brainy Frist was expected to quickly learn the Senate's arcane ways and serve as loyal soldier for most conservative causes.

In some ways he has. Frist has refused to back down in the fight to appoint conservative judicial nominee Miguel Estrada to the federal bench. He also won acclaim from Republicans and Democrats for taking time to hear them out before making decisions. Lott was seen as less inclusive and more of a backroom wheeler and dealer.

For better or worse, Frist has shown a surgeon's attentiveness to order and deadlines. At times, he appears detached from the personal interactions that so often dominate senatorial relations. "Trent Lott would burst into my office, without staff, breathless, talking about what we'd do in the next half-hour," said Senate Minority Leader Thomas A. Daschle (D-S.D.). "With Frist, it's usually a message by Blackberry."

Finance Committee Chairman Charles E. Grassley (R-Iowa), who brokered the tax deal that landed Frist in hot water with Republicans, said: "He's got a very orderly way of leading the Senate, which is a very disorderly institution." Some of Frist's biggest fans are moderates, such as Snowe, and mavericks, such as Grassley, which helps explain why conservatives are grumbling, GOP aides said.

Daschle, who preceded Lott as Senate leader, said Frist can afford to brush off criticism from House Republicans. "House members will need him a lot more than he needs them," he said.

Under Frist, Republicans quickly completed last year's belated budget and passed a ban on what antiabortion activists call "partial-birth" abortion.

Most Republicans appear willing to give Frist more time to master the job before judging him. "In six months, he will be equal to anybody in the ability to handle [Senate] tactics," said Sen. Judd Gregg (N.H.).

Still, the recent setbacks could have long-term political consequences for Frist unless he quickly recoups. He is widely expected to seek the presidency someday, perhaps in 2008. In fact, before taking the majority leader job, his advisers privately expressed concern that the role could interfere with his plans. The recent history of Senate leaders running for president is not enviable.

"There's no doubt Frist has had his eye on national office since Day One," said Scott Reed, a GOP political strategist. "The Lott episode was not part of the plan. He did the right thing by stepping forward and helping the party through it. But it will clearly put his career in some potential difficulty if he can't govern and hold the conservative base together."

The biggest knocks on Frist coming into the job were his lack of political experience and the perception that he was too close to Bush, who many GOP senators viewed as playing an inappropriately strong role in picking Frist as their majority leader. Now the joke among some Republicans is Frist is doing too good of a job proving his independence from the White House.

Allies say Bill Frist is simply unfamiliar with running the Senate.Senate Majority Leader Bill Frist chats with Sen. Debbie Stabenow (D-Mich.), right, during a break in tense tax cut and budget negotiations, which have raised questions about the majority leader among fellow Republicans.