The traditional start of the fall presidential campaign is now behind them, and George Bush and Michael Dukakis, despite their stated desire to take the high road, are showing signs of only intensifying the caustic tone that has become the staple of this year's drive for the White House.

Though they have campaigned frantically all summer, both the Republican vice president and the Democratic Massachusetts governor put in high-profile Labor Day appearances to launch their autumn contest to succeed President Reagan.And while they began on opposite ends of the nation and tried to tell voters about their various dreams for America, neither man could resist returning to bitter and mocking attacks against the other.

It was a tactic mimicked to a degree even by their running mates, Republican Sen. Dan Quayle of Indiana and Democratic Sen. Lloyd Bentsen of Texas, and it probably reflected the fact that the GOP ticket in recent weeks has come from far behind to make the race a virtual dead heat.

The latest of the opinion polls, emerging today from the Boston Herald and WBZ television in Boston, found that of 1,001 likely voters questioned Friday to Sunday, Bush led 46 percent to 43 percent with a 3-point error margin.

Bush, spending Monday in crucial California, began in San Diego and grabbed center stage at a star-spangled sendoff for Olympic athletes at Disneyland in Anaheim, trying to play hard on patriotic themes while portraying Dukakis as soft on defense.

"I wouldn't be surprised if he thinks a naval exercise is something you find in the Jane Fonda Workout Book," the vice president jabbed, invoking the name of the actress and exercise guru whose Vietnam War protests made her a villain to conservatives.

Dukakis, stressing economic issues at a labor rally in Detroit after starting his day in Philadelphia, punched back by recalling that Bush said last week's rise in the monthly unemployment rate was "statistically irrelevant."

"That's not surprising, coming as it did from the standard-bearer of the party that thought ketchup was a vegetable," he sniped.

Quayle, meanwhile, in a minor victory over Dukakis, imitated Reagan's 1980 Labor Day kickoff by speaking at New York's Ellis Island - where Dukakis had wound up Saturday with his immigrant mother after Quayle aides were the first to reserve it for Monday.

Bentsen, speaking in Waco and Beaumont, Texas, echoed Dukakis's economic themes and attacked Bush, who claims the Lone Star State as an adopted home, for failing to look after the interests of the sagging oil industry. Bentsen defeated Bush in 1970 for the Senate seat he currently holds.