NEW YORK, JULY 8 -- Jesse L. Jackson, an unannounced candidate for the 1988 Democratic presidential nomination, received a warm, sometimes raucous reception today at the NAACP annual convention, where he called for the Senate to reject the Supreme Court nomination of Appeals Court Judge Robert H. Bork.

Jackson denounced Bork's nomination, and the convention delegates applauded enthusiastically when he said the Reagan administration "has shifted the civil rights climate from 'we shall overcome' to 'we shall overturn.' "

"Judge Bork's political direction is a threat to the credibility of the court," Jackson said. "We don't need the nominee of a jilted Justice Department confirmed so that we can end up with a tilted court. President Reagan nominated Judge Bork because of his conservative political ideology, and the Senate ought to reject him for the same reason."

The 15,000 delegates attending the NAACP's meeting voted this week to oppose the Bork nomination. They were joined yesterday by John E. Jacob, president of the Urban League.

"If our opposition is based on ideology, then I want to state here and now that so is the appointment," Jacob said.

Bork's selection, Jacob added, would "make a right-wing playground out of the Supreme Court."

In marked contrast to the polite reception accorded Democratic presidential candidates Rep. Richard A. Gephardt (D-Mo.), former Arizona governor Bruce Babbitt and Massachusetts Gov. Michael S. Dukakis in their appearances before the civil rights group, Jackson was given celebrity treatment, sharing the dais with boxer Michael Spinks and Broadway actor Ben Vereen.

Gephardt, Babbitt and Dukakis also told NAACP delegates that they oppose the Bork nomination.

Jackson said someone else, perhaps a Hispanic nominee, should replace Bork as the Reagan adminstration's nominee to the high court.

"We must start a series of unbroken prayer vigils at the Supreme Court until a just justice is nominated," Jackson said.

Jackson outlined a pro-labor platform that he said focused on "a new internationalism" aimed at retaining jobs for American workers and discouraging multinational companies from moving factories elsewhere.

In his 50-minute speech Jackson also referred to the other candidates who have competed for the convention's attention this week, saying that he is leaning toward running because he can "stimulate hope."

Black voters, he said, too often have a "grasshopper complex." "Stop dodging lawnmowers and other people's feet," he said.