The proliferation of candidate debates, with nearly three dozen scheduled before mid-March, has begun to substantially alter the tone, tactics and strategy of a presidential campaign already dramatically different than the last two.

The 20 scheduled Democratic debates and 14 on the Republican side have in large part replaced the ubiquitous straw polls of the 1980 and 1984 campaigns as the major public political events on which the candidates and news media focus prime attention.

That change, politicians of both parties said, could well produce a primary season in which issues gain importance, in which lesser-known candidates have a better chance at competing and in which television presence continues to be a major factor.

The campaign is already unique because of what politicians call "front-loading," bunching together so many of the contests so early in the year, including "Super Tuesday" in March, when 20 states will choose favorites. While that gives an advantage to candidates equipped to raise large amounts of money and to build organizations in many states at once, debates tend to counterbalance that.

"The debates are good for the underdog," said Charles Black, campaign manager for Rep. Jack Kemp (R-N.Y.). "It provides exposure . . . . They are a big part of our strategy for getting Jack known nationally."

"Debates are a great benefit to late starters," said Paul Tully, political director of the campaign of Massachusetts Gov. Michael S. Dukakis (D).

"Regardless of a candidate's organization or money, he's at the same level as the other guys," said David Keene, a consultant to Sen. Robert J. Dole (R-Kan.). "It obviously helps someone not in the front ranks," he added, citing former Delaware governor Pierre S. (Pete) du Pont IV (R) -- a relatively unknown candidate who has staked out controversial stands on such issues as welfare, Social Security and federal aid to farmers -- as a possible beneficiary of the increased number of debates.

The 1980 and 1984 emphasis on straw polls forced news media attention on questions of organization, money and tactical maneuvers, as candidates would spend $75,000 to $250,000 to get their supporters to state conventions, where attendees would vote on whom they preferred for president. While these popularity polls had nothing to do with convention delegates, candidates would use them to demonstrate the strength of their campaigns.

Debates, in contrast, have already functioned to force the news media to focus on where candidates stand on issues and, to a lesser extent, television style and mannerisms. Trade has become a central issue in the contest. After the first multicandidate televised debate in Houston last month, differences in trade policy became the focal point of a dispute between Dukakis and Rep. Richard A. Gephardt (D-Mo.), leading to a well-covered debate in Iowa between the two on the issue. Trade also was the subject of a Kemp-Gephardt debate, and foreign policy the subject of another contest between the two.

Tully, who worked in Walter F. Mondale's 1984 campaign, noted that the straw polls of 1983-84 prompted Mondale to adopt a strategy of "winning everything everywhere, and to bleed down other potential competitors so they would have fewer resources." This year, with the large number of debates, he said, "there is the ability to continue the step-by-step building of an organization while talking to large audiences."

The role of debates may be magnified by the application of high-technology systems that can provide the news media with immediate "results" and hard numbers to evaluate candidate performances.

The Houston debate, for example, was shown on a large screen to 85 probable participants in the Iowa Democratic caucuses in a special focus group set up in West Des Moines. Each participant was given an electronic dial that was used both to evaluate the performance of each Democrat in the debate and, afterward, to judge the candidates on their persuasiveness, intelligence, knowledge and a number of other factors.

It was this process, and the wide publicity it received, that compounded political damage to former Arizona governor Bruce Babbitt, widely believed to have performed poorly, and magnified the benefits to Sen. Paul Simon (Ill.), whose strong stands on issues important to liberals were believed to have helped him in liberal Iowa.

In addition, this technology provided a boost to both Gephardt and Dukakis, whose performances were rated highly by the group. There is a general expectation that this kind of immediate, high-tech evaluation of debates could become an integral part of the 1988 presidential contest.

For the Democrats, the debates are playing an unusual role. Unlike most presidential nomination fights, this one has no clear Democratic front-runner, and consequently none of the candidates has an incentive to avoid debates in order to cautiously protect a strong lead.

"We have a race where even the front-runners are midgets in the public's mind," said Harrison Hickman, a Democratic pollster. "Every one of them needs as much exposure as they can get. Remember who the audience is: people who tend to be opinion leaders, the press, or local pols and contributors and activists. For a formless, leaderless field, that is a critical group right now."

For the Republicans, who have a decided front-runner in Vice President Bush, his willingness or unwillingness to participate in debates and his performance when he does are likely to be major factors in whether a principal challenger emerges.

Lee Atwater, Bush's campaign manager, in an interview played down the importance of debates. "I don't know what they will do to change the ball game," he said. "I'm convinced that the public loses interest after the first debate."

Despite that, the vice president reversed himself last week and agreed to participate in an Oct. 28 debate of all GOP contenders in Houston. His previous refusal to debate that early in the campaign had drawn a chorus of complaints from his competitors and others. Bush has agreed to participate in five later debates.

Debates, while significantly less costly to candidates than straw polls, have forced campaigns to set aside research staff and periods of a day or more to prepare for the public competition.

"The greatest hurdle for {Babbitt} was to look at countless hours of himself on television," said his spokesman, Mike McCurry. "When he was governor, he never treated television very seriously -- the stage was all his." Now, McCurry often follows Babbitt with a video camera so that at the end of the day, Babbitt can evaluate once again the television image he conveys.

Similarly, Kemp privately used a high-tech focus group to evaluate his performance electronically in a debate with Gephardt.

"It forced him to look at what he does well and what he does badly," a Kemp aide said.

Performance in debates has also become another -- some say more valid -- way of judging candidates. "We have very few ways to gauge the candidates. Opinion polls, which everyone knows are unreliable at this stage, and money are the only two measures we have other than debates," said Hickman.

Babbitt and his aides have acknowledged that the political community judged his performance in Houston as poor and that it set back his campaign. "There is nothing that concentrates the mind like the reviews we got," McCurry said. "If you are not a natural, you practice."

While debates have been criticized as superficial tests of candidates, McCurry said they are legitimate: "The next president has to have the ability to work with the American people. You have to be able to communicate in order to lead."Staff researcher Colette Rhoney contributed to this report.