The past five years have seen substantial gains for the Republicans as the party of choice among American voters. Polls show either exact equality between the GOP and the Democrats or statistically insignificant differences.

These trends not only point toward a major alteration of what has been a 50-year, pro-Democratic balance of political power; they also suggest that what partisans of the president call the "Reagan revolution" has a potential degree of permanence. The GOP's hope is that the Reagan coalition -- the 59 percent of the electorate that backed the president's reelection -- will translate into a Republican majority coalition that includes large chunks of what were once Democratic constituencies.

For the Republican Party, and for the prospective candidates seeking the GOP's 1988 presidential nomination, a critical question becomes: What kind of a campaign in 1988 will best serve to convert the Reagan constituency into a more permanent GOP bloc?

Would an insurgent Jack Kemp campaign intended to maintain anti-establishment momentum help firm up the Republican voting base? Or would the party fare best with a George Bush appeal based on loyalty -- the premise being, in the words of a Bush aide, that "the vice president equals the president, therefore be with us"? A third possibility is a campaign based on fiscal restraint and led by Bob Dole with the goal of mobilizing voters concerned about the deficits.

The struggle to become a majority party is forcing Republicans to abandon in general elections what are known as "church" political strategies -- the assumption of a solid, homogeneous congregation of voters who are all conservative, relatively well-off and white -- in favor of "coalition" politics assuming a diverse base some segments of which conflict with one another.

If the Reagan coalition has Republican permanence, its base is now far more diverse, including, for example, a significant number of Hispanics and former "yellow dog Democrats" -- poor white Southerners. A central consideration of Republican strategists is now that the new Republicans do not all attend the traditional GOP political "church" of pro-business, laissez-faire economics, nor do they all have country-club aspirations.

But the core of activists determining presidential nominations remains tied to the "church" style of politics. In 1980, and even more in 1984, GOP convention delegates showed a devotion to conservative goals far deeper than that of many of the operatives behind Reagan. "The Republican presidential primary process remains a right-wing orgy," one key Kemp backer stressed.

The departure of Reagan as a presidential candidate in 1988 will have significant consequences for both the GOP and the conservative movement. "For 25 years," a strategist for Dole said, "the conservative movement has been owned by two people, first Barry Goldwater and then Ronald Reagan. In 1988 the game will be different for the first time in a generation. No one will hold fee-simple title to the Reagan constituency."

It is in this highly fluid universe that the two leading contenders, Bush and Kemp, along with Dole, Baker and Delaware Gov. Pierre du Pont, are mapping strategies for 1988.

A central element in Bush's strategy is the quiet acquisition of party support, particularly from members of a group known as the "Reagan Rogues" or, if their political histories date back to the 1964 presidential campaign of Barry Goldwater, the "hard core."

These are men and women who challenged the Republican Party establishment to back Goldwater 21 years ago, or backed Reagan in his earliest bids for the presidency, in 1968 or 1976. Bush strategists are counting on the backing of these activists to give Bush the conservative credentials he needs in order to gain the nomination.

"There are a lot of people out there who hated George Bush in 1980," a Bush supporter said. "He was the guy who challenged Reagan, who said he came from Texas, but was born in New England. But a lot of those people are going to be with George Bush in 1988."

Bush's lineup of public and private supporters reportedly includes a good number of solid Sun Belt Reaganites (not all of them, incidentally, Bush "haters" in 1980). Although generally unknown to the public, in the "church" politics of Republican presidential nominations, they are the bishops of the right. One of them, Tommy Thomas of Florida, endorsed Bush on the assumption that he has become a Reaganaut by osmosis: "Five years of association with Ronald Reagan have been very good for him. . . . He is so loyal to the president; that's why I'm supporting him."

Kemp, in turn, is caught in a delicate position. He is attempting to challenge Bush as the legitimate heir to the Reagan legacy, while at the same time presenting himself as a politician who can significantly expand the Republican base. He, more than any other candidate, is campaigning directly on the realignment issue.

This makes for an interesting, and potentially risky, style of campaigning. Kemp, for example, pointedly broke with Reagan over the trip to the Bitburg cemetery in Germany, and he initially was sharply critical of the administration's tax reform bill.

Bush aides are attempting to capitalize on these dissents by arguing that they amount to an attack on Reagan. In an attempt to undermine Kemp, a Bush supporter said: "People at the White House say Kemp's always there, except when you need him."

Kemp is trying to portray himself as being at the cutting edge of a new and growing Republicanism. While perhaps appealing to the younger converts to the GOP, and to some of the hard-core conservatives who see themselves as on the vanguard of a conservative American revolution, such public declarations pose the danger of alienating traditional Republicans. Kemp drew a number of querulous stares when, at a recent gathering of midwestern Republican officials, he opened his remarks to the almost entirely white, upper-middle-class audience of stolid churchgoers with: "Welcome fellow revolutionaries."

Perhaps even more challenging to conservative dogma, Kemp tells audiences: "If we just run against government, if we make government the arch- enemy, we lose sight of the fact that many people look to government as a source of security. . . . The good shepherd loves the flock but also the stray."

Kemp strategists contend that Bush's successful efforts to acquire the endorsements of party officials, even those with solid Reagan credentials, may backfire in a political party that has gained its momentum in part from a deeply rooted anti-establishmentarianism. "Losing the endorsement sweepstakes may be a blessing in disguise," John Buckley, Kemp's press assistant and deputy press aide to the Reagan-Bush '84 Committee, argues as he compares Bush's endorsement tactics to those of Walter F. Mondale in the 1984 campaign.

Kemp aides contend that the changes in caucus and primary procedures initiated largely by Democrats over the years have simultaneously functioned on the Republican side to severely restrict the power of party leaders and to open up the system to a challenger such as Kemp.

But, as one Kemp supporter acknowledged, "It's tough to turn a challenge to a Ronald Reagan clone (Bush) into a revolution within the Republican Party."

In this highly fluid universe, such less prominent contenders as du Pont and Dole are calculating that there is more room to maneuver, particularly if neither Bush nor Kemp can catch the Reagan spirit among those Republican activists who become delegates.

Strategists for Dole, who ran into severe opposition from conservatives because of his support for raising taxes in 1982, now argue that his image remains vague enough that "it can be shaped."

Dole has used his position and his battles over spending cuts to gain influence with Senate colleagues and with traditional Republicans concerned about the size of government. Dole is pointedly opening up the Senate floor to legislation on the conservatives' agenda, in a move that might quiet some of the past anger at his tax policies. "He's going to give some of these issues (a balanced-budget constitutional amendment, a presidential line-item veto, relaxed gun controls) a chance to be heard, issues Howard Baker kept in the deep freeze," an aide said.

In this context, presidential pressures on all the prospective candidates are likely to prompt steps that go beyond the range of speeches to GOP groups and endorsements, to substantive legislation, particularly in the terrain of the social issues -- abortion, school prayer, etc. -- which have, in the main, received short shrift in a government now run by a Republican Senate and the most conservative president in two generations.