NEWS ANALYSIS : Bush Uses Jabs at Clinton to Help Own Credibility : Speech: The combative style reflects magnitude of President’s task of closing gap with his rival.

For three days and nights, Republicans told voters why they should not vote for Bill Clinton for President. Sounding every bit the underdog he has become, the President of the United States picked up Thursday night where they had left off--and, almost as an aside, told America why it should vote for George Bush.

In an acceptance speech that gave a bitter tenor to the start of the autumn campaign, Bush heaped scorn on his rival’s credentials as would-be commander-in-chief, and painted him as a spend thrift steward of the nation’s economy.

The biting tone and hard-edged strategy reflected the magnitude of the task at hand for Bush and his reelection team as they try to close the gap on their front-running rival. While seeking to raise new doubts about Clinton, Bush needed also to resolve voters’ old doubts about himself.

“Good judgment comes from experience, and experience comes from bad judgment,” Bush said, at once challenging his rivals’ credentials and apologizing for breaching his own “no new taxes” pledge.

As he sought to make amends for first-term mistakes, Bush said in essence that his second term would be better. What had gone wrong on the domestic front was Congress’ fault; gridlock would give way to reform.

And to those who might remain unconvinced, he suggested that the alternative would be to relive an unhappy history. A Clinton Administration, he said, would bring a return to “a rubber check Congress and a rubber stamp President.”

In many ways, what Bush sought to confront in his prime-time address were the same challenges that have faced his campaign since it began: why the nation remains saddled with domestic problems despite his stewardship, and how he might offer a way out.

But he levied the attacks on Clinton before beginning his answers. And the answers were little more than the premise he has been trying to persuade voters to accept for months: that he has offered a plan; that a recalcitrant Congress stood in the way; and that his reelection could usher in a new wave of reform.

Still, his pledge to press for an across-the-board tax cut offered voters perhaps the clearest picture yet of his idea of change in his second term--one in which a Congress chastened by a Bush victory would allow him to embark on a more activist course.

The decision by Bush to dig in his heels in perhaps his most important speech ever was a gamble that he could make voters believe that the ideas he has long embraced offered the best solution to the nation’s problems.

“The truth is the truth,” he insisted. “Our policies haven’t failed; they haven’t been tried.”

But as he presented his vision of government beyond November, Bush was careful not to offer the kind of specifics that might alienate important voting blocs.

He pledged to impose a cap on entitlement spending--a proposal which theoretically could affect veterans, or Medicare recipients, among others--but did not say which programs would be affected. And his bold-sounding call for a tax cut was tempered by the assurance that he would do nothing to add to the federal budget deficit.

Bush chose the most fundamental of terms to compare his plans to his rivals’. “Theirs is to look inward, and protect what we already have,” he said of the Democrats’ vision. “Ours is to look forward.”

The combative speech--and its cutting characterizations of Clinton and his proposals--set the stage for a blunt autumn campaign in which the President is expected to hold little back.

As signaled by Bush and summed up Thursday by his pollster, Fred Steeper, Bush’s approach calls for “offering a better plan, and convincing people that Clinton’s plan would be a disaster; and as bad as things are, (the Democrats) would make them even worse.”

Bush rejected suggestions that he use the speech to unveil bold new proposals. Aides had feared that such a course would mark an admission of failure. In fact, the cuts he called for in taxes and spending have been part of his agenda for most of the election year.

His decision to base his campaign on programs that so far have found little resonance left Bush open to criticism that he was offering only more of the same.

“The test of a good issue is not whether you have heard it before or not,” campaign Chairman Robert M. Teeter said Thursday in outlining that cautious approach. “I have no problem with repetition in politics.”

For Bush, the speech marked perhaps his best chance before expected autumn debates to overcome the imposing lead Clinton has achieved in public opinion polls.

He used the 56-minute speech--virtually the same length as Clinton’s acceptance speech last month--to offer his most complete rendition of his general election message: that he is best equipped to turn affairs around.

“It is not a denial that the problems exist,” Teeter said. “It is which way you can go in trying to fix the problems.”

That strategy reflects a conclusion that, no matter what Bush does in the next 10 weeks, most Americans will go to the polls in November still convinced that the nation is on the wrong track.

But Bush sought also to play what his aides regard as his political trump, devoting a major portion of the address to reminders of his foreign policy triumphs and warnings that it would be foolhardy to trust new perils to inexperienced hands.

He mocked Clinton as the “leader of the Arkansas National Guard.” And he contended that his rival sought to have it both ways in announcing his opinion about the Gulf War--two days after Congress had “voted to follow my lead.”

“While I bit the bullet,” Bush said, “he bit his nails.”

Bush advisers say such close attention to foreign policy, even in a year in which voters rank the issue near the bottom of their concerns, serves two purposes:

It casts Bush as a leader whose successes abroad are evidence of his capacity to lead at home. And it points out the enduring importance of foreign policy, the issue on which Clinton’s inexperience leaves him vulnerable.

“No voter in the country will go to the polls without knowing that the single most important thing a President does is to conduct foreign policy,” Teeter said. “Before we’re done on Nov. 3, that will be a significant point of every voter’s decision: whether they feel comfortable with these guys in conducting foreign policy. And on that issue we’ll win 10 to 1 or 20 to 1.”

Still, advisers said Bush’s most important task--both in the speech and for the duration of the campaign--was to gain credibility on a platform of change. Advisers spent weeks trying to find ways to craft language that could somehow convince voters that this incumbent President and 30-year political veteran stood for true reform.

“If the election comes down to change vs. change, we lose,” a senior Administration official said. “But we can win the debate if we can elevate the debate to competing agendas.”