Decisive action by Walter F. Mondale apparently has brought the Rev. Jesse L. Jackson into his fold as a working supporter of the Mondale-Ferraro Democratic Party ticket for president as a first step to revive sagging black interest in the Mondale campaign.
Many black voters have expressed disinterest in the Mondale campaign since last July's Democratic National Convention. Restless, newly registered ''rainbow coalition'' backers of Mr. Jackson say the Mondale-Ferraro campaign organization has ''neglected'' both Jackson, who ran third in the Democratic primaries, and ''black issues.''
Such black leaders as Mayor Andrew Young of Atlanta have labeled the Mondale drive ''insensitive to the hopes of black people.''
Mr. Mondale made his key move Sept. 29 when he broke his schedule to fly from Atlanta with Jackson to make a surprise appearance before 3,000 diners at the closing banquet of the 14th Congressional Black Caucus Weekend in the nation's capital.
The Democratic presidential candidate made a positive impression on an audience that was honoring Jackson as recipient of the Adam Clayton Powell Award , bestowed by the nation's 21 black members of Congress.
Since that meeting Jackson, showing the spark of his fiery primary campaign, has spoken out strongly for Mondale.
''I support Mondale because he supports social justice,'' Jackson told a campus audience at the Memphis State University field house Oct. 4. He shared the platform with Democratic vice-presidential candidate Geraldine A. Ferraro, who has since appeared with other black leaders as she tours the South.
Jackson also aroused audiences at a $1-a-plate bean supper in Houston Oct. 2, and at various stops in Mississippi.
These appearances contrasted with the lukewarm backing Jackson had delivered since the party convention. He was emphasizing black support of local and state candidates, mentioning Mondale only once or twice in his speeches.
The Democratic National Committee also took steps to recover waning black support, publishing a guide (''Blacks and Democratic Politics'') and holding a briefing session for black campaign workers.
Key black leaders in the Mondale-Ferraro campaign - among them Mayor Andrew Young of Atlanta; Maynard Jackson, former mayor of Atlanta; US Rep. Charles Rangel of New York, and Ernie Green of the Jackson campaign - gave pep talks to 500 black workers from around the nation Sept. 29. They assured them that Mondale can win ''in spite of what the polls say.''
Larry Little, a city alderman in Winston-Salem, N.C., is the kind of person whose support the Democrats are trying solidify. He says: ''The (Democratic Party) convention disappointed me as a black person. It gave other special groups - women, Hispanics, the Hart people - something. It left us blacks out.''
The pace of black voter registration has slowed drastically in Winston-Salem since the convention. Prior to the North Carolina presidential primary in May the number of blacks registered in the city jumped from 22,000 to 31,000. Since July only 200 blacks have been added to the voter rolls, says Mr. Little.
Black support will rally behind Mondale, asserts George Dalley, deputy campaign manager for issues development, the highest-ranking black in the original Mondale organization.
''Our basic problem is to get rid of the defeatist attitude,'' he says, adding that, with the renewed activity of Jackson and other leading Democrats recently, ''everything looks brighter to me.''