For all the talk of the love fest between Texas Gov. George W. Bush and Arizona Sen. John McCain, the first glimmers of what soon could be more heated competition between the two Republican presidential rivals appeared at last night's debate in Phoenix.

Both candidates, who are running neck-and-neck in New Hampshire, have pledged to run positive campaigns and have gone out of their way to be nice to each other. They were last night. But in the debate, McCain also began to tell Republican voters that he and Bush have differences in both policy and experience.

Last night's debate was generally friendly. Magazine publisher Steve Forbes and Utah Sen. Orrin G. Hatch each praised former diplomat Alan Keyes on taxes. Former Reagan administration official Gary Bauer praised McCain on campaign finance reform. Hatch effusively praised Bush for appealing to Hispanic and African American voters.

With five candidates on a stage in Phoenix and McCain participating by satellite from Boston, the debate was also in some ways less contentious than their first joint encounter in New Hampshire last week. Despite a format change that allowed the candidates to question one another directly, the barbs were limited during the 75-minute debate hosted by CNN.

Bauer directly challenged Bush on China and trade. Forbes attempted to force Bush to choose between the oil producers of Texas and the heating oil consumers of New Hampshire. The competition on the right appeared as spirited as the competition between Bush and his rivals, with Bauer and Keyes offering strong performances. That raises the question of whether their exposure could hurt Forbes, who hopes to consolidate the right.

But it is the Bush-McCain dynamic that now dominates the Republican nomination fight, and with time growing shorter, the Arizona senator appeared determined last night to begin to separate himself more clearly from Bush.

At one point, Bush, citing his own emphasis on giving faith-based institutions more federal money and encouragement, asked McCain for his views. McCain used his response to that question and a follow-up to draw several distinctions with the Texas governor.

First he made clear that while he, like Bush, supports school vouchers, he would not drain away any federal money currently earmarked for education from public schools, as Bush's plan would do. Instead, he said, he favors using money gained by ending federal subsidies to big industries to fund a pilot plan. It was another way for McCain to reassure voters who worry that vouchers will hurt public schools while also claiming the reform mantle he so cherishes.

McCain also took a direct shot at Bush's new tax plan, which calls for $483 billion in cuts over five years--a bigger plan than the one passed by the Republican-controlled Congress but vetoed by President Clinton. McCain suggested the plan might be irresponsible.

Asked by Bush whether he supports a particular element of his new plan, McCain responded: "Sure I agree with that. . . . But there's a big difference. I do not envision surpluses forever. . . . I don't know that we're going to have surpluses forever." Instead, McCain said, he would attempt to pay for his own tax-cut plan by reducing spending and corporate subsidies.

McCain also sought to display the breadth of his knowledge of the world and foreign policy, a not-so-subtle attempt to play off criticism that Bush is inexperienced in world affairs.

At one point, Bush, who mentioned last week that he was reading a biography of former secretary of state Dean Acheson, was asked what he had learned from Acheson that he would apply to his own presidency. When the questioning turned back to McCain, the senator made a detailed reference to Acheson briefing President Harry S. Truman on North Korea invading South Korea.

Later, after Forbes had asked Bush how he would try to drive down rising oil prices, McCain used an unrelated question to offer an answer that Bush had not talked about, once again displaying his foreign policy credentials.

McCain drew a link between future oil supplies and the Russian bombardment of Chechnya, saying it was crucial that U.S. policy be geared to preserving access to oil in the former Soviet republics in Asia. "I'd pay attention to what's happened in Chechnya," he said.

As in the first debate, Bush did nothing that is likely to cause a major reevaluation of his candidacy. Nor did he dominate this event any more than he did last week's debate or the speaking contest at the Iowa straw poll, the only other times he has shared the stage with his rivals.

If he sounded scripted at times, however, there were other moments when it was clear he had made some adjustments, apparently seeking to avoid criticism that he had spent too much time talking about Texas.

Last night he continued to refer to his record, particularly on lowering taxes, an issue important to Arizona and New Hampshire voters. But he spent more time talking about what he wanted to do as president, and he stressed both his conservatism and his compassion.

Seemingly mindful of McCain's appeal as a man who said last night "there ain't going to be the status quo when I'm president of the United States," Bush also invoked the reform theme in describing his agenda. "I've got a record of reform in the state of Texas," he said.

The debates represent in some ways the education of George W. Bush and ultimately the Republican voters in the key primary and caucus states that will administer the grades. But last night John McCain served notice that he may be ready to step up and test Bush directly. If that happens, the Republican race will get even more interesting.

Staff researcher Ben White contributed to this report.