The betting here is that Ronald Reagan will not run for reelection and that, absent the Reagan mortar and magic which hold it together, the Republican Party will split into at least six warring and unequal factions.

Most recent presidents first determined to win the White House some time around Thanksgiving of the second grade. But Reagan was different. Reagan did not run for any public office until he was 55 years old, and only after he had had a full and satisfying career in films and the actors' union. Quite unlike many recent chief executives, Reagan's self-worth does not hinge on his riding on Air Force One for five more years.

Entirely different impulses motivated the last two elected Republican presidents, according to Marty Nolan of The Boston Globe. In Nolan's judgment, Richard Nixon ran for president to be something; Reagan ran for president to do something. And Reagan has done it. As evidence, the Democrats are emphasizing their plans for improving economic growth rather than for imposing economic redistribution. Reagan has changed the American debate.

In 1984 the Republicans will not win the House and could well lose the Senate. A second term could very well be both a personal and political letdown for the president. But the Reagan Revolution is not in imminent danger of being repealed. No Democratic candidate is advocating national dental insurance or federal takeover of the cost of school crossing guards.

Reagan owns the heart, the mind and the glands of the Republican Party. To oppose him for renomination would be an act of political self-immolation that no elected Republican is considering. But only that Reagan magic and popularity can restrain the warring groups now coexisting most uneasily under the GOP banner. When Reagan withdraws, civil war will follow.

First, consider the divisive social and cultural issues. Libertarian Republicans are totally laissez faire on all matters of personal behavior, up to and including the smoking of South American cigarettes. Ardently opposing the libertarian Republicans are those energetic followers of Sen. Jesse Helms who would just as soon codify all human behavior, and may soon advocate appointment of a federal commissioner of heavy necking.

Somehow the president himself can manage to be simultaneously both the champion of a balanced budget constitutional amendment and an unreconstructed supply-sider undistressed by a $200 billion annual deficit. But a lot of traditional Republicans, and other assorted Americans, are quite bothered by grossly unbalanced budgets. Just as a lot of unconventional Republicans are still practicing supply-siders. Another gulf. Some Republicans are pro-business (for governmental involvement like the Chrysler loan guarantee) while others consider themselves free enterprisers, believing with Eastern Airlines' Frank Borman that capitalism without bankruptcy is like Christianity without hell. In the matter of selling to the Russians, Republicans again split, with many arguing that principle should come before profits in policy as well as in the dictionary.

Without Reagan to maintain harmony, the 1984 GOP presidential fight will be a brawl. And it could be so bitter that the prize isn't worth having.