CHICAGO, AUG. 2 -- Divided in their choice of a Democratic presidential candidate, grass-roots activists vowed today to mobilize against Senate confirmation of Judge Robert H. Bork's appointment to the Supreme Court.

The weekend "retreat" of about 1,200 organizers of consumer, civil-rights, feminist, environmental and "public-interest" groups wound up this noon with Sen. Edward M. Kennedy (D-Mass.) whipping up enthusiasm for the fight against President Reagan's latest court nominee.

Kennedy derided the White House "public-relations campaign to portray Robert Bork as a moderate conservative. Those public-relations advisers must be smoking Admiral Poindexter's pipe," he gibed.

Neither Kennedy nor Sen. Alan Cranston (D-Calif.), who also spoke today, offered any assurance of success in blocking the appeals court judge Reagan has picked to succeed retiring Justice Lewis F. Powell Jr.

But Ralph Neas, executive director of the Leadership Conference on Civil Rights, told a crowded strategy meeting this morning it is "a winnable fight," with 25 to 30 senators on the fence.

Neas and Ricki Seidman, legal director of People for the American Way, cautioned the mostly youthful left-wing organizers not to emphasize a few issues, such as abortion rights and affirmative action, but to criticize Bork's overall record of "radical conservatism," as Seidman termed it.

Neas predicted that the Senate Judiciary Committee, which starts hearings on Sept. 15, will be so closely divided it will "probably agree to report the nomination {to the full Senate} without a recommendation."

"You'll see very little movement until after the hearings," Seidman cautioned the organizers. Uncommitted senators "feel they have to appear to be fair-minded, so you should push but not pressure."

"Don't be heavy-handed," Neas agreed. "Do everything you have to do, but in a low-keyed way." He said Bork's rulings on cases involving corporations and consumer issues -- emphasized by Kennedy in his speech -- would allow "a populist campaign" that might be particularly effective in southern and midwestern states where many of the swing Senate votes are concentrated.

The civil-rights, feminist and economic issues involved in the Bork nomination make him a natural target for the organizers of about 25 grass-roots groups meeting here under the common banner of Citizen Action and the Midwest Academy, a Chicago training school for activists. They found far less agreement on the choice of a presidential favorite after hearing six of the eight declared and possible Democratic contenders seek their support.

Heather Booth, president of the Midwest Academy, said in an interview that Jesse L. Jackson, who drew perhaps the strongest emotional response from the group, is "a leader, if not the leader, of progressive forces in America," who has made himself "a partner of many of our state organizations in their struggles."

But she noted that Rep. Richard A. Gephardt (D-Mo.) "has worked with us on farm, health and energy issues," that Sen. Joseph R. Biden Jr. (D-Del.) has Mike Lux, a popular veteran of the Citizen Action effort, organizing for him in Iowa, and that Massachusetts Gov. Michael S. Dukakis (D) "has strong support from some of our allied groups," notably senior citizen and union groups in Massachusetts.

Sen. Paul Simon (D-Ill.) was endorsed last week by the Illinois Public Action Council, one of the largest of the Citizen Action affiliates, and Booth said she expects "state-by-state decisions" over the next few months.

"It's premature to expect consensus now," she said, "but I think it's a very healthy process of testing the candidates' views and their electability."

Ira Arlook, the codirector of Citizen Action and head of its Ohio affiliate, reflected the satisfaction of the leftist activists at their growth in size and influence. He told the closing session today that the 1.5 million contributors to the state affiliates now exceed the number of givers to all the national Democratic Party committees and approach the number of contributors Republicans can claim.

As a result, he said, "we've made the leap from hassling local officials to hosting presidential candidates."