Democratic National Chairman Paul G. Kirk Jr. told the NAACP today that blacks and other constituencies in the party must exercise "self-discipline" over divisive internal disputes so that Democrats can be a majority party that is not estranged from black America.

Speaking the day after Republican National Chairman Frank J. Fahrenkopf Jr. was booed here for describing blacks as an "isolated" group because they were almost alone in opposing President Reagan's reelection, Kirk thanked blacks for "voting your principles" in backing the Democrats.

But after drawing laughter with political gibes at Fahrenkopf, Kirk set out in tough language the need for blacks to quiet dissension among Democrats in order to reassure voters that the party can handle its affairs and is ready to govern.

"Where internal struggles may arise regarding procedure or turf," he said, "this will not be allowed to obscure the fact that Democrats care far more about the daily struggles of Americans who work to earn a living, to buy a home . . .

"Each political constituency -- so vital to our party -- must execute its own measure of self-discipline," he said. "Each must look beyond its own agenda to a larger vision of a strong, united party marching and leading the nation forward."

Kirk reassured the delegates that their 90 percent support for the Democratic ticket last year would not be taken for granted.

"We will concentrate on policies that unite us as a majority party in America but we will never abandon our commitment to minority America," he said.