Both political parties seem to be having a hard time finding enough top-quality congressional candidates this year. Black organizations are having a hard time increasing significantly the number of black public officials, since it is hard to create more black- majority legislative districts given population decline in ghetto areas and dispersal of blacks to the suburbs.

These two political problems can both be solved, at the same time, if both Democratic and Republican organizations would recruit blacks to run for Congress and other offices in white-majority districts. If I were advising either party, I would say that one of the best ways to win an otherwise difficult seat is to run a black candidate, even if the district contains a negligible number of black voters.

There is certainly no lack of attractive, highly qualified blacks, particularly in the age group that produces most first-time congressional candidates (30-40). The problem for the parties is that these blacks are already doing well (law firms, corporations, the media have all been bidding for them), and they fear that they will be rejected by white voters.

This fear is almost certainly unfounded. A Washington Post survey of blacks found that young, educated blacks are especially likely to see whites as unrelentingly racist and hostile; yet every survey of whites--and their voting behavior as well --shows this is wrong. Few whites are going to elect a black who bills himself as a ghetto radical, or a white candidate with similar attitudes. But they are willing to elect a black who is not out of line with their own issue positions and even one whose positions on civil rights issues are advanced.

The prototype of the future black officeholder will not be the ghetto militant, but the mainstream politician with relatively few black constituents -- Mayor Thomas Bradley of Los Angeles or former Sen. Edward Brooke of Massachusetts.

From a party's point of view, a black candidate has two advantages. First, he will get noticed. There is enough novelty in a black candidate in a mostly white area so that a black candidate will get more exposure than a comparable white. Second, a good black candidate will tend to exceed the expectations of many white voters. It is always a pleasant surprise when a candidate turns out to be smarter, more pleasant, and more sensible than a voter expected.

Some white voters won't support a black. But as old people die and younger people begin to vote, there are fewer every day. After all, voting for a black candidate for Congress is one of the easiest ways to prove you're not a racist.

The most difficult problem for the parties is to motivate the right kind of black candidate. Almost by definition he is already living the good life. Why should he give it up for the long hours, hectic routine, and iffy chances of a congressional candidate?

He should do so for the same reasons other candidates run: some mixture of idealism and ambition. The idealism we are assuming is already there. As for ambition, to understand how it works, you have to understand that every white male candidate has a daydream, which he confides to no one, that some day he will be president of the United States. After all, Spiro Agnew made it from the zoning board to the vice presidency in only six years, and Richard Nixon made it from nowhere to the vice presidency in the same time.

Until now such daydreams have not been plausible for black (or female) candidates. But these things are changing fast. The country is probably ready to accept a Jewish vice president (Ed Koch surely daydreams about it), and California may very well elect a black governor. We accept women mayors of Chicago and Houston. You could have gotten marvelous odds just 10 years ago against any of these things happening in this century.

It is in the interest of both political parties to convince talented young blacks that the voters will be ready for a black president sometime in their lifetime, and to get them started daydreaming about running for Congress this year, then moving up to the Senate in 1988 or 1990, and then . . .