The early withdrawal of Sen. Robert Dole from the Republican presidential race this week clearly means that the GOP nominating campaign is over even though the party convention is not for another 41/2 months.

Of course, the convention vote Aug. 15-18 is needed to make Vice President George Bush's nomination official, but barring a major catastrophe, that vote is no longer a real issue.Dole's withdrawal leaves only former TV evangelist Pat Robertson in the party race, but he has won only 17 delegates to date against Bush's 788 of the necessary 1,139. Most of Dole's delegates are expected to move into the Bush camp. Robertson has already said privately that he is aiming at 1992.

The early ending is something of a surprise. The campaign for the GOP nomination had been expected to be a longer, closer battle. However, Bush's near-shutout of Dole in all of the primaries since the Iowa caucuses rapidly changed that picture.

It's hard to explain that landslide, but most experts believe Dole hurt himself in the early going by getting a reputation for caustic comment. Except for a run-in with TV newsman Dan Rather, Bush spent much of his effort avoiding trouble or mistakes.

As a result, he has come across as a vague figure, lacking any real charisma, although his credentials in public service, ranging from terms in Congress to a variety of high posts, including CIA chief, and seven years as vice president certainly are impressive. Public opinion polls usually rate him as "steady," rather than exciting.

President Reagan has held himself aloof from the campaign, refusing to take sides with any candidate, saying he would wait until after the GOP convention. But with Bush essentially having wrapped up the nomination, the president may join the fray earlier than expected.

Despite his lopsided win, the vice president faces some unusual problems. For instance, the Iran-Contra trial may be in the news all summer, hardly a political benefit to the administration's No. 2 man, no matter how it turns out.

In addition, Bush may have difficulty campaigning against a specific opponent for several months.

While the Democrats obviously would prefer to have a presidential candidate chosen before their July 18 convention begins, it may come down to a convention floor struggle.

Whether Bush's early victory and additional time to prepare for the presidential race will be an advantage, or whether the Democrats will reap the benefit of more attention because of their on-going delegate battle, is hard to say.

As Bush grapples with these imponderables, it's increasingly apparent that an easy victory can pose as many problemns as one that must be fought down to the wire.