The first Republican presidential primary of 1988 may very well be held -- more than a full 18 months before either Iowa or New Hampshire -- in Dallas July 2-4, 1986. Those are the dates for the planned, but not yet formally announced, National Conservative Convention, which is the project of John T. (Terry) Dolan, director of the National Conservative Political Action Committee (NCPAC).

Complete with state delegations composed of representatives, as one meeting planner puts it, of "the separate religious, economic and defense- foreign policy wings" of the contemporary conservative movement, the convention is expected to feature speeches by presidential hopefuls and the first straw poll on 1988 candidates. It is a nationally televised prospect that has some Republicans shuddering.

In the past 20 years of presidential politics, most nonnegotiable demands have been made of Democratic presidential candidates. It always seemed to be at a Democratic convention that the pert spokesman of the "transvestite taxidermists" was threatening a walkout of his caucus and that some terminally unsmiling militant feminists were insisting on a platform endorsing retroactive abortion for white males to the age of 35 -- "or else!" The Democrats, upon whom such demands were visited, nearly all remembered their party's 1968 convention, which turned into a nationally televised riot and which helped Hubert Humphrey lose the presidency. Striving at any cost to avoid another Chicago, the Democrats have since sued for peace with just about any organized group that threatened a convention protest.

But this approach has given most special-interest groups what they demanded in the Democrats' platform and helped to give the Republicans the White House on a semi-permanent basis. As Democratic presidential candidates have painfully discovered and as Republican candidates could get their own chance to learn in Dallas next July, special-interest endorsements can be a blessing during the spring primaries and a curse in the fall election.

After Ronald Reagan's two presidential landslides, the political importance of the constituencies conservative groups claim to represent cannot be easily discounted. For example, according to the CBS-New York Times exit poll of actual voters, a full 15 percent of the November 1984 electorate describe themselves as "born again Christians." Reagan carried this group 4-to-1 over Walter Mondale. Or to look at it another way, one-half of the Reagan victory margin (as well as one out of five of Reagan's total vote) came from voters who described themselves as "born again Christians."

One unique legacy of the Reagan Revolution is that the leaders of these moral-political groups are now regular visitors at the White House and frequent guests on the network news shows. As political leaders, they enjoy a reserved place at the national Republican head table and, understandably, expect to be courted and consulted by GOP politicians who would be president.

This could produce a real problem for Republicans at Dallas next July. For all special-interest groups -- whether the Moral Majority or the National Council of Senior Citizens -- there is always an organizational imperative to have an agenda that no presidential candidate can rationally grant. Otherwise, there would be little reason for the continued existence of either the organization or, heaven forbid, its direct-mail fund-raising appeal.

This is the dynamic that can lead to nonnegotiable demands on politicians. Obviously, no organization in this modern era of information overload can "deliver" its membership's votes. But for 1988 GOP candidates, mindful and envious of those Reagan numbers among born-again voters, the temptation to do some concentrated wooing could prove irresistible.

Next Fourth of July in Dallas could turn into a political-cultural trade show, with presidential candidates issuing statements about how they literally believe that Jonah survived in the tummy of a whale or how they would ban homosexual custodians from federally funded housing projects, not to mention the abolition of child labor laws and the nuking of Havana. All this and a straw ballot too.

For 1988 GOP candidates, the question about the Dallas convention of July 1986 may turn out to be whether they can afford not to go or whether they can afford to go.