How does a president celebrate the Fourth of July? It may be a holiday for millions of ordinary Americans. But it will be a workday for President Reagan as he sets out from Washington on a three-day swing to rouse the spirit of national patriotism - and, not incidentally, to hobnob with blue-collar workers and court their vote in the November election.
Independence Day 1984 will find the President attending the Firecracker 400 Stock Car Race and a picnic in Daytona, Fla. Then he flies to Huntsville, Ala., for a ''Spirit of America'' Independence Day festival. The following day he travels to Detroit for a series of events at General Motors plants. The trip ends Friday with an address in Dallas to the Texas State Bar Association convention.
Demonstrating the advantages of incumbency, Mr. Reagan will be politicking merely by being presidential. As he sounds the themes of a sturdy economic recovery, a strengthened American military posture, and a restored national pride, the President will in effect be asking Americans to contrast his stewardship of the country with that of Jimmy Carter and his vice-president, Walter Mondale.
Forays into the Southern states are especially important to election strategy , Reagan political planners say. In 1980, Reagan captured the South as voters turned their backs on President Carter. But with the emergence of the Rev. Jesse Jackson as a Democratic presidential candidate and the registration of many new black voters, the Republicans are working hard to make sure they hold the South, where they won by only narrow margins in a number of states.
A primary focus of that effort has been a massive drive to register new voters sympathetic to Reagan, capitalizing on the white backlash to the Jackson phenomenon. The drive has paid off, with registration of some 800,000 new voters nationwide, many of them in the South. At the moment, say GOP operatives, Reagan is running far ahead of Mondale in the Southern states.
''The appeal of Jesse Jackson to blacks has stimulated a lot of people to register for Reagan,'' says James Lake, a spokesman for the Reagan-Bush campaign committee. ''There's a real fear (among whites) that, if new black candidates appear, the power structure - the sheriff, the county clerk, and others - can get turned out of office. So there is a definite turning to our candidate, and we have a strong show of support.''
In wooing the labor vote, campaign planners say, Reagan is mainly addressing the rank and file instead of the union leaders, who have largely endorsed Walter Mondale. Mr. Lake says some effort will be made to persuade local labor leaders at least to refrain from attacking the President, knowing that his support among labor remains strong. A recent survey by Reagan pollster Richard B. Wirthlin showed the President leading Mondale among blue-collar workers by more than 50 percent.
Michigan, which went for Reagan in 1980, remains one of the most economically depressed areas of the nation despite a comeback in the auto industry. It will be one of the major battlegrounds in the fall election campaign, and this is why the President is giving it attention.
The economy is seen as the most sensitive issue. In Detroit Mr. Reagan is expected to preach his message of economic resurgence, including a dramatic drop in inflation. Despite the recent half-point rise in the prime rate to 13 percent , President Reagan's political advisers continue to voice optimism that this is only a temporary phenomenon and that interest rates will begin to decline between now and the election.
''We think it will increase a bit to September and then come down,'' says a high administration official. ''If the economy continues to improve, and the inflation rate holds, the fact that interest rates are higher will not hurt us too badly. But we are worried about cutting off the recovery in housing and autos.''
As the President prepares to celebrate the Fourth, his popularity seems to loom as an almost insurmountable obstacle to Democrats.
A Gallup poll released over the weekend showed Reagan jumping to a 19-point lead over Mondale. The survey, taken June 22-25, gave the President 56 percent and the anticipated Democratic nominee 37 percent.
According to the poll, Reagan leads Mondale among men and women in all age categories and in all sections of the country. He is especially strong among voters under the age of 30, leading Mondale by 33 points. He also leads among independents by 66 to 24.
Despite such rosy poll results, the President's political strategists play them down and warn Republican campaign troops against engaging in euphoria. A key adviser says that Reagan and Mondale now have an equivalent number of votes in the states in which they lead. The President's advantage is that in the states where he is ahead (i.e., the Rocky Mountain States), he has a more solid margin of support.
''I'm not sanguine about the election,'' says the adviser. ''This is the year for a close election. Mondale will come out of the convention only four to six points down and will therefore close the gap.''
Other themes to be stressed by the President as he woos labor and other important constituencies are ''family values'' and ''peace.'' Campaign strategists believe that Reagan has proved wrong the Democratic charge and public concern that he is a ''trigger-happy cowboy.'' Nowhere, they say, are American troops involved in combat overseas.
In recent months Reagan has used every occasion to point up that, while his administration has built up US defenses and made America stronger, it is doing everything possible to improve relations with the Soviets.