President Reagan plans to focus his political efforts during the next six months on raising money and helping candidates in key states, but he is prepared for early participation in the presidential campaign if a clear-cut GOP choice emerges, according to White House and GOP strategists.

Reagan's official position is that he is strictly neutral in the GOP primary contest and will not become involved in the presidential campaign until a nominee is chosen at the Republican National Convention in August.

However, sources close to the president said that Reagan's personal choice for the nomination is Vice President Bush, whom the president has repeatedly praised. And these sources said Reagan is prepared to start campaigning this spring for Bush or any other Republican presidential candidate if it appears that one of them has a lock on the nomination because of his performance in the primaries.

"If it became clear we had a de facto nominee, the timetable could be moved up to involve the president as early as late March," said one White House official.

A strategist outside the White House observed that Reagan is well aware from his own experience of the "snowball" effect of primaries once a candidate takes a commanding lead. In 1980, Reagan emerged as the front-runner with a decisive victory in the New Hampshire primary late in February and in effect sewed up the nomination in the March 18 Illinois primary.

Strategists say Reagan is prepared to step in and try to play a unifying role if the GOP is scarred by the wounds of a harsh primary campaign.

"What makes 1988 unique from the president's perspective is that you do not have one overriding political objective but multiple objectives," said Frank Donatelli, the White House political adviser. "We're trying to help the party at all levels."

Donatelli said the president has agreed to a three-part plan that includes helping state parties raise money; making appearances at events designed to help Republicans win or retain control of state legislatures in some key states, and campaigning for some Senate candidates.

Some events will combine all three purposes -- and more. On Feb. 11 Reagan will fly to Los Angeles and speak to a Republican event aimed in part at helping Sen. Pete Wilson (R-Calif.). The next day he will make a brief trip to Mexico for a meeting with President Miguel de la Madrid, and he will then take a three-day holiday at his ranch northwest of Santa Barbara, Calif.

Reagan plans to make two political trips a month through August. This will mean a busier-than-usual travel schedule for Reagan, who also is expected to attend a NATO meeting in Europe in early March, a summit in Moscow this spring and the economic summit of the seven industrialized democracies in Toronto in late June.

But the White House and the Republican campaign committees plan to make more selective use of Reagan, who turns 77 on Feb. 6, than in 1986, when he campaigned across the country in an unsuccessful attempt to keep the Senate in Republican hands.

Reagan, then at the height of his popularity, tried to transfer it to Republican Senate candidates, saying over and over again that "you can vote for me one last time" by casting a ballot for the GOP candidate.

"Neither Reagan nor those advising him understood that you can't transfer political popularity in that way," said a Republican strategist close to the president. But White House officials say it would also be a mistake this year to go to the other extreme and conclude that Reagan's involvement in the campaign is unimportant.

"Presidential involvement is a necessary but not a sufficient condition," said one official. "Just because Ronald Reagan says, 'I want this fellow' doesn't mean he would make it. But there is clearly a group of voters who will pay attention to the Reagan endorsement."

White House officials said Reagan understands that any GOP nominee will necessarily differ with him on some issues, as even Bush has on occasion in the primaries. "I think the president realizes that voters aren't looking for a carbon copy of him or anyone else," said one official. "You have a different situation and different issues than in 1980."

Reagan nonetheless is said to believe that the election of a Republican president and Bush in particular would be a ratification of his "legacy" on basic issues of foreign and domestic policy.