I am a direct-mail specialist who has worked on behalf of several score Republican candidates and organizations in the past 10 years, including three presidential efforts (Ford '76, Bush '80 and Bush '88).

Hence, I'm reluctant to share trade secrets with the Democrats. However, The Post's Sept. 12 editorial regarding direct mail and Pat Schroeder's decision on a presidential campaign compels me to comment on two points:

Almost every article in The Post that addresses direct-mail fund-raising portrays direct-mail contributors as supporters of "narrow" or "fringe" interests, be they left or right. Further comments usually suggest that only candidates of an extreme position benefit from direct-mail solicitations.

Perhaps this idea is merely a reflection of the fact that The Post's usual source of such information is either Roger Craver (liberal) or Richard Viguerie (conservative) or one of the many "clone" consultants their respective agencies have spawned.

True, there are many supporters who base their financial support solely on one or two issues. Yet the vast majority of the Republican Party's contributors tend to be "traditional Republicans," the kind of folks who consistently support the Republican cause -- not individual causes that fall under the Republican banner.

Your own editorial comes close to pointing this out by citing how the Republicans "depend less on inflamed appeals." In fact, the "inflamed appeal" approach has been tried many times -- and generally produces far less income than appeals oriented toward good government and Republican boosterism.

This fact is further borne out by noting that the combined national Republican donor base numbers some 2 million to 3 million supporters. Perhaps that's only 2 percent of the eligible voting population, but the number exceeds the base population of several states -- and thus is hardly a group of "narrow interests."

A final indicator that direct mail is not limited to "extreme" candidates is the success of efforts we have managed for candidates ranging from Sens. Charles McMathias to Arlen Specter, Warren Rudman, Dave Durenberger, Rudy Boschwitz, Pete Wilson, Frank Murkowski, John Heinz, Charles Percy and Bill Armstrong. No political expert would lump them together as "extreme," yet all have benefited from direct mail.

Concerning Schroeder's financial base -- and, for that matter, the financial base of all presidential contenders -- the secret of success is to avoid dependence on any one form of fund-raising.

Direct-mail support takes on added significance in a presidential effort because of the "matching funds" quotient: small donations double themselves due to matching fundsfrom the government. Even so, candidates must also attract broad support frommid-range givers ($100 event ticket-buyers) and big givers ($1,000 major donors and PACs).

In 1980, Ted Kennedy depended almost exclusively on $1,000 donors; without small-donor support, his campaign ultimately faced financial difficulty. John Anderson, who found personal major-donor solicitation distasteful, depended exclusively on small-donor direct-mail givers; like Phil Crane and others who counted on small-donor direct mail, the level of support was not enough to sustain his candidacy for the duration.

By comparison, the campaigns of Gerald Ford, Ronald Reagan and George Bush have thrived financially because they deployed a "mix" of fund-raising efforts -- mail, telemarketing, events and major donor efforts. The value of this broad-based fund-raising strategy became especially evident to Ford andBush when their primary campaigns suf-fered political setbacks at the polls: their ability to hang in and continue was largely due to the consistent flow of income from differing sources (large givers early on, small givers later).

This kind of strategy is less trade secret than it is common sense. Thus, Schroeder -- like every other presidential contender -- ought to take a hard look at her fund-raising strategy and base. Failure to do so still haunts Gary Hart, John Connally and John Glenn.

Timothy L. Roper