Let Reagan be Reagan. That seems to be the judgment of Republican leaders as they assess the political fallout from the first presidential debate and consider GOP campaign strategy in the few weeks remaining to the election.
Instead of loading the President with statistics and figures in a debate in order to show somehow that he knows his job, say party stalwarts, he should do what he does well: use the symbols and images of office to convey his strong leadership and sense of values and keep pointing up the principal accomplisment of his presidency - economic recovery - as the key to an election victory.
''He was overcoached in the debate,'' says Andrew Natsios, chairman of the Massachusetts Republican State Committee. ''He should simply be himself and articulate his economic program, which is the cutting edge of the party realignment going on. Then he'll do well in the rest of the campaign.''
Privately, GOP leaders concede that Reagan strategists miscalculated in assuming that Democratic challenger Walter Mondale would aggressively go on the attack in the debate and therefore trying to alter the President's normal approach. The net result, some say, is that Reagan tired from the burden of a ''facts and figures'' approach and showed weariness for the first time. The concern is that this may become an election issue.
''The biggest liablity that could be blown up is his age,'' said a state party leader who did not wish to be identified. ''His stumbling appeared to be that of a senior citizen rather than a sharp opponent.''
Officials of the Reagan-Bush campaign committee say confidently that there is no need for a campaign reassessment. They anticipated a ''momentary blip'' in the ratings for Walter Mondale, they say, and the news media changed their own debate standards by suggesting, first, that Mondale had to deliver a ''knockout blow'' and then saying that the President had to deliver such a blow. Mondale did nothing but solidify his own base, they add, and a tightening of the race by Nov. 6 is expected.
The only change on the campaign trail, say Reagan operatives, is that the President will go on the offensive attacking Mondale's ''mistakes'' on such issues as income-tax indexing and medicare, and zeroing in on the Mondale tax-increase plan. In the debate Sunday the Democratic contender set the agenda on the economy, with the result that Reagan did not manage to make economic recovery the centerpiece of the evening or effectively attack the Mondale tax.
''One thing that comes out of the debate is a change in the way we go out on the offense on Mondale,'' says John Buckley, deputy spokesman of the Reagan-Bush campaign committee. ''The message we feel was loud and clear from Mondale is that he represents the old tax-and-tax and spend-and-spend policies, and we will repeat this over and over.''
Reagan will keep to his schedule this week, going out to Michigan Wednesday and to Ohio on Friday, where he will duplicate the Truman whistle-stop trip of the 1948 campaign - even riding the same train. ''It's just full speed ahead with the same campaign strategy,'' says Charles Black, an independent Reagan adviser. ''Although it appears to people that Mondale won the debate and the President did not do well, people will not change a lot of votes.''
At the same time, the Reagan forces will use the first debate to fire up the troops in the field, say campaign officials. From the time of the GOP convention a major concern of the President's campaign has been overconfidence and complacency out on the hustings because of Reagan's huge leads in the polls across the country.
Also, the President's White House advisers will be carefully thinking through the second presidential debate and how to respond to Mondale's unexpected strategy. Many political experts say that pressure now grows on the President to acquit himself well in the second debate, especially since foreign policy, the sujbect of the debate, is not his strong suit.
How much an issue age may or may not be come is not clear. ''If the Democrats go after that they do so at their own peril, because the American people see a vigorous President, and his performance on Sunday was one of a virogous man,'' says Mr. Buckley.
Presidential historians say age has not been a critical factor in any prior election. Nor has there ever been a president who spent his 70s in office. Reagan was 69 when he took office; Eisenhower was 70 when he left.
''Probably voters will instinctively think about that. Reagan came off looking tired,'' says Robert Murray, presidential scholar at the University of Pennsylvania. ''I don't think (the age issue) will be articulated. ... But the debate put it in the picture where it wasn't there before.''
Nonetheless, Professor Murray and other analysts believe that economic well-being will be the overriding consideration as Americans go to the polls. On this account, they still see a decisive Reagan victory.