POLITICAL experts say that it will take time, but that the rhetoric in the New York City mayoral campaign is sure to heat up as the November election approaches. New Yorkers, used to combative politics in their high-energy city, will likely take it all in stride. Until now both Democratic nominee David Dinkins and Republican nominee Rudolph Giuliani have been portraying themselves as decent men who hate crime and drugs and who can bring all the diverse elements of New York City together.
If the first day after their primary win is any indicator, however, a change in campaign strategy in both camps may already be under way. The attacks to date have been gentle. Mr. Dinkins accuses his rival of being a ``Reaganite'' Republican while Mr. Giuliani describes Dinkins as a ``clubhouse'' politician.
Former federal prosecutor Giuliani is under the most intense pressure to adopt a tougher stance. He faces an uphill battle.
Dinkins, for example, who is the city's first black major-party mayoral nominee, won a large one-third of the white Democratic vote.
It has been 24 years since a Republican, John Lindsay, won the New York City mayoralty. If Ronald Lauder, Giuliani's defeated primary opponent, holds to his pledge to run on the ballot as the Conservative Party candidate, he will likely siphon away Republican votes from Guiliani.
A former federal prosecutor, Giuliani faces the strong united opposition from Democrats critical of some of the tactics he used in prosecuting cases and of his lack of administrative experience.
``Giuliani has a lot of enemies,'' says Demetrios Caraley, a professor of political science at Barnard College. ``If he continues to try to be a nice guy, I think he'll get about 20 percent of the vote.'' Dr. Caraley says he thinks Giuliani's ``only chance'' is to build up his image as one who is tough on crime.
``My guess is that we'll see Giuliani try to drive a wedge between Dinkins and either his black base or between Dinkins and Jewish voters in some fashion,'' says Norman Ornstein, a political scientist with Washington's American Enterprise Institute.
Dinkins may not prove as vulnerable to political attack as Giuliani may hope. He is by now a familiar face in New York politics. A former state legislator and New York City clerk, he was elected Manhattan borough president on his third attempt. Efforts to tag him with failure to pay his income taxes between 1968 and 1972 have been politically unsuccessful.
Dinkins's Democratic colleagues are now solidly behind him. Some are critical of his deliberative, low-key approach. Yet that nonthreatening manner is also part of his appeal to ethnically diverse New Yorkers. ``I think his overall image as a conciliator will work to his advantage,'' Dr. Ornstein says.
Still Dinkins, who points out that he served in the US Marine Corps, is also under pressure to adopt a more aggressive campaign stance.
Ornstein offers some advice: ``If I were running against Giuliani, I'd attack him on his supposed strength as prosecutor. I'd focus on grandstanding that looked much more at Wall Street crime than at street crime - and on the fact that he clearly overreached in some cases and was far more sensitive to his own public image than to the rights of others.''
In the primary, both Dinkins and Giuliani were ``nice guys'' who happened to finish first. In November, however, much their campaign tactics change, one of them will finish last.