It was a very odd speech Jesse Jackson delivered to the founding convention of the Rainbow Coalition last weekend in Washington. The fiery minister, who broke ground two years ago as the first major black contender for the presidential nomination, abandoned his rhyming rhetoric and personalized political sloganeering. For most of his hour on stage, he was the Organization Man.

"Ideas flow from the head," he told the thousand or so delegates, "but power flows from operational unity . . . . We must build the vehicle for the expression of our interests and power." The instructions for his new vehicle were as complicated as an "easy-to-assemble" Christmas toy.

"Each state organization will be chartered by the National Rainbow Coalition, and will register with their secretary of state. The state organizations will be able to recognize affiliates," he began, sounding for all the world like some franchising executive.

Jackson has a well-earned reputation as a seat-of-the-pants operator, able to stir crowds to near-frenzy but incapable of building a structure that can survive in his absence. What was he doing talking Harvard Business School jargon?

The answer is that he is "moving on up," as he likes to say. He is making ready a vehicle more substantial than the jerry-built network of preachers and activists he mobilized in 1984, for what will almost surely be another presidential candidacy in 1988. Scorning the "sandlot politics" of his past, he vowed, "The Rainbow Coalition will have rules and discipline. . . . (It will) be an effective vehicle in the political arena."

"What comes out of this," said Lamond Godwin, a top aide in the last campaign, "is intensive organizing for a national convention in 1987, at which he (Jackson) will either announce his candidacy or announce support for someone else. Between now and then, there will be very serious planning for another campaign."

So much for the hopes some Democratic leaders have entertained that they would be spared another round of infighting with Jackson. He has been invisible at party meetings since 1984, but he has been busy on his own, tapping the constituencies of discontent. He has been working over alleged bias in the media, especially television. And he has spent a great deal of time in the hard-hit Midwest farm communities. White farm contingents gave this past weekend's convention much more of a Rainbow cast than most of Jackson's 1984 rallies.

There are mixed views on the desirability of another Jackson candidacy among blacks who backed him last time. Richard Adams, a Pittsburgh school board member, was one of many delegates who said, "I hope he runs again. Nothy and hope in the black community than his candi- dacy."

But state Rep. Tyrone Brooks of Atlanta, who was chairman of the 1984 Jackson campaign in Georgia, said, "We made our point in '84, and there's nothing to be gained by doing it again. If Jesse wants to work on issues and build an organization, he can be a vital part of the effort. But it would be a mistake to raise and dash people's hopes again."

A senior black member of the House of Representatives, after asking for anonymity, said he feared a second Jackson candidacy would be "even more divisive" than the 1984 race. "This time, the white candidates will have to be tougher on Jackson . . . . They saw what happened to Mondale when he tried to accommodate him. The white voters just walked away."

The bottom-line fear expressed by this man is: "Will blacks vote in November (1988), in the numbers we need, for a Democratic candidate who beat up on Jesse? Will whites boycott a Democrat who didn't?"

Implicit in his comment is the belief that Jackson is a polarizing figure, not because of his color but because of his hot personality and his radical views: his prediction, for example, last weekend that President Reagan's "assault on the middle class is laying the basis for a social explosion."

But these doubts are unlikely to deter Jackson, for he and his advisers think he has been handed a great advantage in the new southern states' "super-primary" scheduled for mid- March of 1988.

The scheme of having at least nine Dixie states vote on a single day was hatched by white politicians of that region to help a moderate-conservative contender. But it could quite conceivably provide Jackson a wealth of delegates through a plurality victory over a large and divided field of white candidates.

Jackson recalled last week that in 1984 he "finished first in Virginia, South Carolina, Mississippi and Louisiana, second in Maryland, Kentucky, Arkansas and Texas." Nearly all are expected to be part of the "super-primary."

Godwin said the concentration of all those states early in the nomination calendar "gives us an advantage we didn't have before. It goes to our strength. It overshadows Iowa and New Hampshire (the first caucus and primary states, which have few blacks). It's a real nice idea, and we didn't have to promote it. They just handed it to us."