Jesse Jackson is already making the presidential race more exciting. He'll enliven the debates. And he will likely come into the convention next year with just enough delegates to be able to argue strongly for including a black agenda in the Democratic platform.
Since he made his decision to run known, it has become clear to political observers that more than anything else Jackson's entry probably blocks Walter Mondale's effort to lock up the nomination early.
Mondale had a strong arm on the black vote. But no more. One longtime Democratic political activist says that Jackson will win some 55 to 60 percent of the black vote and that that, of itself, will deprive Mondale of some primaries he otherwise would have won.
Oh, yes, Mondale has the black leaders - the mayors and local and state black political leaders - in his corner. Thus, as Robert Strauss points out, Jackson in courting the black vote ''must take on Coleman Young, mayor of Detroit, who is one tough, smart guy. And he has to go to California and take on Los Angeles Mayor Tom Bradley, who is one very effective man, too. But I think Jesse will figure out a way to do it.''
Strauss added: ''I want to remind you that Jimmy Carter took away the black vote. Carter took Coretta King and Andy Young and put them on the road with him. He went into every community and he plucked the black vote away from their leaders. They were for others.''
Jackson has the Democratic political chieftains quite worried, although they certainly aren't saying so publicly. They have had long meetings discussing what to do. Their concerns center on the following:
* They see Jackson, supported by a ''respectable'' number of delegates, pushing his ''black agenda'' before a national TV audience at the convention - an agenda that will be largely big-spending programs that the Democratic Party wants to avoid from now on.
How to turn down such an agenda without alienating Jackson and black voters? Or how to accept such planks without losing the support of millions of Democrats who simply think the time for big spending is over?
* They also see some Jewish leaders asking that the national Democratic Party publicly decry Jackson's evenhanded position in the Mideast, where he is strongly backing a homeland for the Palestinians.
The problem again: how to accede to or resist such pressure without incurring the wrath of one important voting bloc or the other?
* Finally, the party leaders are concerned about what Jackson may do in the debates among the candidates. Known more as a ''movement man'' than a politician , Jackson just might ''ask dangerous, embarrassing questions,'' one such leader says, privately. ''He could be a loose cannon. He might be big trouble in the debates.''
In the short run, the Jackson candidacy hurts Mondale and helps all the other candidates. In the long run his presence and get-out-the-vote efforts might help the eventual winner of the nomination. Or Jackson may be like a bull in a china shop, making it more difficult for any Democrat to win in 1984.