President Bush is exercising one prerogative of being president: changing his mind.

But when a president changes his mind, the ramifications can be far-reaching and sometimes costly.For instance, Bush planned to spend last weekend at his vacation home in Kennebunkport, Maine.

He was to make a four-day event of it, with education speeches in Union, N.J., on the way up and in Rochester, N.Y., on the way back.

Bush delivered the speech in New Jersey on Thursday but scrubbed the long vacation weekend in Maine so he could be on hand for Friday's unveiling of a budget compromise with congressional leaders.

Then he added a new destination for Monday, scrapping upstate New York for Hamtramck, Mich., where he announced a package of economic incentives for Poland.

White House aides wanted a locale with a large Polish-American population, and Rochester didn't quite fit the bill.

Canceling the Kennebunkport trip meant dozens of reserved hotel rooms - obtained by White House aides, security agents and reporters - had to be ditched at the last minute, and a fleet of five dozen rental cars returned.

It also meant elaborate advance and security preparations in Rochester, where Bush was to visit an Eastman Kodak plant and speak at a school, went for naught.

Last month, a planned trip to California and other Western states was scheduled, then postponed and finally canceled. Now, the West Coast trip is on again - but in modified form, for later this month.

Bush flip-flops, of course, include more than trips.

On semiautomatic assault rifles, Bush initially said he opposed any attempts to control or restrict them. But he later moved to suspend imports of these weapons.

Then, he tightened that ban, angering congressional gun-control opponents in the process, amid hints that the administration would come out with permanent new restrictions on both domestic and foreign-produced assault weapons.

He admitted to "a pulse change" on the subject of gun control.

Bush also did an about-face on federal involvement in cleanup operations in the Alaska oil spill, first praising Exxon for the job it was doing and voicing opposition to a federal takeover; then moving a week later to put one in effect.

Bush also executed a turnabout on U.S. funds for the Nicaraguan Contras. First he echoed the Reagan administration position favoring continuing military support for the anti-government rebels. But he wound up going along with a bipartisan agreement sharply scaling back U.S. support for the Contras.

But Bush, after all, is the president. And there's no prohibition against changing his mind, either on trips or on issues.

And kinder and gentler only goes so far. "If you're too polite in life, you get stomped on," Bush told a youngster who was hesitant in raising her hand at a question-and-answer session at the White House.