HANOVER, N.H. -- At half time of the two-hour Dartmouth debate, managers of Sen. Robert J. Dole should have been ecstatic that their man at long last was tearing into a rattled Vice President George Bush. Instead, they were uneasy.

Although the vice president for the first time in four televised debates had slipped when he confused warheads with missiles, Dole was coming over as the grim reaper. Seated in the front row, campaign manager William Brock told his candidate: For goodness sake, Bob, smile! No politician changes his overall appearance more by merely smiling than Dole, and his posture for the second hour here was considerably less foreboding.

Still, the Dartmouth debate epitomized Dole's problems. It was his most aggressive and Bush's least masterful performance. The vice president partially reinforced the old theory that he was at risk in an unstructured atmosphere. The focus of this debate unquestionably was Bob Dole. But even when smiling, Dole was so menacing a presence it was questionable whether the focus helped or hurt him against the front-runner.

Bush's managers always have sought minimum contact with his opponents -- unsuccessfully. His lead never has been comfortable enough to reject debates, and he has performed in more of them than he once thought imaginable. But until Dartmouth, he avoided blunders, basically for two reasons: first, he was superbly prepared; second, Dole -- eager to shed the hatchet man's image -- had restrained himself.

The answer, according to Dole's managers, is to get the vice president in the open field where superb preparation does not matter so much. The best, the senator's advisers say, would be a one-on-one Bush vs. Dole, but that is impossible in a six-man field. So, the Dole campaign has sought a debate format where careful scripting is less possible.

That format presented itself here, where the vice president's agents killed cross-candidate questioning but did not prohibit roundtable discussion. Dole was primed to challenge claims by a Bush campaign flyer of how much the vice president accomplished during the last seven years. The theory was that Bush could not parry an unexpected shot.

Dole actually only challenged Bush's claim of being instrumental in Social Security reform (''I don't think he attended a single meeting''), and the vice president just grinned in response. Bush ran into trouble from Pat Robertson, who pulled from his pocket a transcript of the Houston debate in November where the vice president declared the INF Treaty would destroy warheads when in fact it was missiles.

On television, Bush looked stricken and insisted ''we're taking out 1,600 to 400 of theirs.''

''Of their what?'' asked Robertson.

''Of their vehicles that blow people up, their bombs,'' said Bush.

''No, not bombs,'' said Robertson, ''not bombs. That isn't true.''

Gen. Alexander Haig confirmed that the INF Treaty permits the preservation of Soviet warheads that can be used in long-range missiles directed against the United States, but Bush stubbornly insisted later in the debate that the treaty reduced warheads.

Peter Teeley, Bush's communications director, came into the press room after the debate to read a ''guidance'' asserting that the warheads are ''dismantled'' under the treaty. In fact, there is no such provision in the pact or means of verifying it. But Teeley's intervention was sufficient to persuade political reporters, unfamiliar with arms control exotica, to steer clear of the subject.

Even so, the vice president was off balance for the rest of the two hours. Less certain is how well Dole, smiling or not, took advantage of it. One problem was that not only Bush but also Jack Kemp and Pierre du Pont were in his sights.

Moreover, while Kemp is uncomfortable in the sniper's role, he asserted that ''every answer to every hard question for Sen. Dole is to raise taxes.'' Bush's state chairman, Gov. John Sununu, entered the press room after the debate to declare that Dole now had been branded as a high-taxer.

With both leaders showing vulnerabilities and Kemp rising in the polls in New Hampshire (though not Iowa), the news media's certainty that the Republicans have a two-man race may be premature. Bush first said no to the Feb. 14 League of Women Voters Debate in New Hampshire just two days before the primary, but now cannot afford to pass it up. If Bush stumbled without falling at Dartmouth, Dole must now consider how hard he can afford to be in tormenting the vice president.