SAN FRANCISCO -- An eerie serenity pervades the upper echelons of George Bush's presidential campaign. While Republicans across the ideological spectrum fret that prospective Democratic nominee Michael Dukakis is being allowed to set the pace and agenda of the contest for the White House, Bush and the handful of advisers who are charting his course seem almost nonchalant about the challenge that confronts him.

''I'm very relaxed,'' the vice president said during an interview in the front cabin of Air Force Two, flying out of here the other day. ''It's too late,'' he added with a smile, ''to be anything else.''

In truth, Bush and his inner circle of strategists -- pollster Robert Teeter, chief of staff Craig Fuller, campaign manager Lee Atwater and longtime friend Jim Baker, the Treasury secretary -- argue that it is much too soon to worry about the early Dukakis poll leads that have made other Republicans nervous. They said that before a couple of polls last week showed Dukakis' margin dropping from double digits down to five points or less. And they will continue to say it if the Democrat's lead increases, as they think it will, immediately after his formal nomination in Atlanta two weeks hence.

Watching the Bush campaign, many Republicans and neutral observers have concluded that it lacks theme, direction or strategy. But conversations with Bush and some of his key advisers suggest that they are operating on assumptions different from those of their critics about the timing, the tasks and the basic nature of this election. Agree with them or not, the campaign makes more sense if you understand those assumptions.

As to the timetable, Bush believes that voters won't really start to focus on the choice between Dukakis and himself until the conventions have been held, the vice-presidential tickets have been completed and summer vacations have come to an end. ''Labor Day,'' he says, ''is when the campaign begins.''

Until then, he and his advisers say, the main task is supplying information about the candidates. There's plenty of evidence in polling and interviews to support the view that voters have only a hazy impression of Bushand know even less about his challenger.

On every trip, Bush tries to disperse what he chooses to call ''a lot of froth out there about my elitist background.'' At one stop, he talks with compassion about the ''throwaway'' AIDS babies his wife has held at a Harlem hospital; at another, he slips into corduroy jacket and chino slacks to sympathize with drought-stricken Wisconsin cattle farmers.

But it's not all that benign. In the last few weeks, Bush has begun to do a number on Dukakis, risking an increase in his own already high negatives by personally throwing mudballs at his rival as a permissive, soft-on-criminals liberal.

Once he has a running mate and his other chosen surrogates in place, Bush says, ''the Red Meat Brigade will not have me as its leader.'' But the attack on Dukakis will escalate. ''We may unleash a couple of governors to put it {Dukakis' record} in better perspective,'' Bush says.

The opponent Bush calls ''a cool customer'' will, in the Bush camp's view, try to ''belly right up to Bush,'' by presenting himself as a moderate Democrat advocating only such universally popular changes as a stronger attack on drugs. ''If he {Dukakis} gets away with 'We can do better' speeches,'' says one Bush adviser, ''we lose. We have to make the point there are big differences between these guys.''

The other imperative is to bring the traditional issues of peace and prosperity back to the center of the voters' consciousness. Right now, polling shows the anomaly of large majorities giving Ronald Reagan high marks for reducing the threat of nuclear war, saying they're optimistic about their own economic futures -- and still believing that the country is seriously off on the wrong track.

Bush says he thinks much of that is caused by ''the new threat to stability of the family and the community -- narcotics.'' Advisers say it's broader, a ''feeling the social fabric is being torn apart'' by the very pace of change in the economy, in the schools and in families.

Ultimately, I suspect, it's that question of change which may decide whether Bush or Dukakis wins this election. As the out-party candidate after a two-term presidency, Dukakis automatically is in a strong position to bid for the constituency of change.

But Bush and his advisers don't believe that most Americans will ultimately vote for much in the way of change. ''People want to feel better about things like homelessness, education, child care and narcotics,'' Bush told me. ''They want to see progress, and progress means change. But they don't want radical change, or fundamental liberal change.''

One of his strategists puts it this way: ''I think people would like to have a difference without a whole lot of change.''

The Bush message will be that you can't have ''a whole lot of change,'' of the kind Dukakis symbolizes, without risking the peace and prosperity of the Reagan years. But you can have a modest difference, with a bit more emphasis on repairing the fraying social fabric, with Bush.

It's hardly a bold strategy. But it is a strategy.