"Black power," the militant slogan, has been in eclipse for a decade or more. Black power, the political fact, may be entering a period of significant growth.

So, at least, says Eddie Williams, president of the Washington-based Joint Center for Political Studies and a seasoned observer-analyst of political trends. Williams, who is black, likes what he sees.

"Circumstances have conspired to give the black vote enormous potential power in the November elections," he says, citing "good prospects" both for increasing the number of blacks in Congress and for increasing black influence on white candidates.

Williams isn't guaranteeing immediate congressional gains (though he will bet you a drink that the Congressional Black Caucus won't slip from its present high of 18 members), but he thinks the trend is clear.

Item: Mississippi, where a black state representative has won the Democratic nomination in the majority-black 2nd district, may be sending a black to Congress for the first time since Reconstruction.

Item: South Carolina Democrats have nominated Ken Mosely, a black college professor, to challenge six-term Republican Rep. Floyd Spence. The district, whose hub is Columbia, is 35 percent black.

Item: Georgia's 5th district (Atlanta) seat, currently held by the "fairly liberal" Democrat, Wyche Fowler, has been targeted by Julian Bond, who has said he may run as an independent if he does not win the Democratic nomination.

"The South is emerging as a crucial battleground for blacks in this fall's election," Williams contends. Even where no black candidate is running, black voters should have substantial influence, he says, citing the latest Census Bureau statistics showing blacks comprise 20 percent or more of the population of 60 southern congressional districts, many of them newly reapportioned.

"Blacks may prove to be a swing vote in several southern districts where incumbents rode the Reagan coattails to narrow victories in 1980," Williams believes. These first-term Republicans--including Albert Lee Smith of Alabama, Eugene Johnston of North Carolina, Thomas Hartnett and John Napier of South Carolina, and Thomas Bliley of Virginia, may face tough reelection battles.

Most of the growth in black political power is in the South, which now has seven more districts with populations 20 percent or more black than it had following the last reapportionment in 1972. The Northeast has nine such districts, two fewer than a decade ago, while the number in the Midwest (13) and the West (4) remains unchanged.

Still, according to Williams, there are at least two non-southern districts in which black candidates have a decent shot at victory: Alan Wheat, a black Missouri assemblyman, has won the Democratic nomination to succeed retiring Rep. Richard Bolling, and black attorney Orville Pitts is given a reasonable chance in a "wild" six-way primary battle to succeed retired Rep. Henry Reuss in Wisconsin's 5th district.

Edolphus Towns, black, is favored to defeat two Hispanics in a primary fight to replace Brooklyn's Fred Richmond, who resigned in a personal scandal. Two black state senators, Vander Beatty and Major Owens, are vying to succeed Shirley Chisholm, guaranteeing that that seat will remain black in spite of Chisholm's resignation.

The only Black Caucus member to be hurt by the latest reapportionment was Missouri's William Clay, whose St. Louis district was redrawn to include a white suburb, reducing the district's black populaton from 65 percent to 52. Even so, Clay has won a tough primary fight with racial overtones and is expected to defeat black Republican Bill White in the general election.

Williams cautions that the black population percentages can be somewhat misleading. First, the Census Bureau's numbers don't cover voting- age population, which may be smaller for blacks than the general population figures suggest, and second, even blacks who are eligible to vote may not vote in numbers sufficient to transform their potential power into actual influence.

He concedes the truth of what Lowell Weicker told the recent convention of the NAACP: that blacks have "hurt themselves by staying at home, and that is what the bigots and the racists of the world are counting on."