Jesse Jackson finally has found an office other than the presidency worthy of him. He is negotiating with Sen. George Mitchell, the majority leader, to acquire the key to unlock the gates of social justice.

And what is this glittering prize? Floor privileges in the U.S. Senate for Jackson, soon to be ''Shadow Senator'' from the District of Columbia.

Undaunted by the fact that the office does not yet exist and will have no power when it does, Jackson has announced his candidacy and has taken his election as a formality not to be waited on. He has set out to settle something far more important to him than power: perquisites.

(He is punctilious about tokens of respect. Two years ago he made his party hostage to his epic pout about not having received a timely telephone call from Michael Dukakis concerning his, Jackson's, non-selection as vice-presidential nominee.)

If (Jackson says demurely -- if) elected, he will seek privileges enjoyed by real senators, including the right to roam the floor -- and a desk there at which to sit when roaming stales -- and space in a Senate office building. Speaking of access to his soon-to-be semi-colleagues, the real senators, Jackson says, ''We certainly want to have access to them. We deserve it.''

''We''? Is that the regal (papal?) plural? Who is two? ''Me and my shadow''? Perhaps it is a state of mind.

His Shadowship will be a lobbyist for statehood for the District. He will be a play-acting senator for a make-believe state.

The District is only a city, and only of moderate size. It is the nation's 16th-largest and, because of restrictions on its growth, it will continue to descend the list of largest cities as others grow. The Constitution provides for three kinds of entities: states, territories and the District. States are the fundamental entities of this federal system. Senators represent geographical areas containing diverse interests.

The District as a state would be different. It would be the only state with no rural interests whatever; no mining or other extraction industries; no fishing; almost no manufacturing. But lots of government.

The decay of Jackson's career into burlesque is part of a pattern of dereliction of leadership among prominent blacks. Benjamin Hooks, head of the NAACP, recently suggested to 3,000 convention delegates that the prosecution of Washington Mayor Marion Barry -- star of videotape and Louis Farrakhan rallies -- is part of the government's ''incessant harassment of black elected officials.'' It was not the first time Hooks had cast that aspersion or the first time he had no evidence to support it.

During an NAACP convention panel discussion of blacks in the entertainment industry, one panelist delivered an antisemitic diatribe, which, the Los Angeles Times says, ''drew enthusiastic applause from many in the audience,'' Not surprising, that. When many prominent blacks like Jackson cannot bring themselves to denounce Farrakhan, anything can be said, so long as it is said against someone who can be blamed for blacks' problems.

Nowadays when many black leaders speak, they do note the pathologies of the black community and exhort it to cure itself. But those admonitions seem perfunctory and secondary to the cultivation of the aura of victimhood and the denunciation of victimizers (Jews, the Justice Department, whites generally). Such black leaders are becoming more boring as their charges become more lurid.

The posturings of an ersatz ''senator'' or a conspiracy-monger like Hooks are multiplying as the need for unpleasantly truthful talk is becoming more pressing. Three truths are:

Many blacks and others suffer from what sociologists call insufficient ''social capital,'' a deficit of the skills requisite for both economic competence and successful living.

Second, we know little about how to use social policy to generate the social capital that cures the behavior of poverty, when such capital has not been produced by the nurturing of an intact family.

Third, we know what does not help -- demagoguery such as Hooks's or grandstanding such as His Shadowship's.

In 1796, when Tennessee was on the verge of statehood (which the District of Columbia hardly is), two Tennessee senators arrived prematurely. A contemporary letter says:

''One of their spurious senators has arrived, and a few days since went into the Senate and claimed his seat, by virtue of the credentials from our new sister Tennessee, as she is called, and the rights of man. As the former was a new kind of coin, and the latter has often been declared, and even counterfeited by rogues and rascals, a majority of the up-stair folks determined to take time to inspect both, and with some difficulty persuaded the bearer to leave them.''

George Mitchell, please note.