EVEN BEFORE Michael Dukakis' defeat last November, Democratic pollster and campaign consultant Paul Maslin was warning that "the next four years will be extraordinarily difficult for the Democratic Party," in part because of the long shadow Jesse Jackson casts over the next presidential campaign. Maslin said the civil-rights activist has to be considered the early front-runner for the 1992 nomination. Agreeing, longtime Democratic strategist William Galston said, "He has a base and no one else does." In addition to the experience and constituency Jackson gained in his last two races, he stands to benefit in 1992 from rules concessions he extracted from Dukakis at the Atlanta convention. Those changes reduce the number of delegate votes given automatically to party leaders (who, in 1984 and 1988, voted overwhelmingly for Jackson's remaining white opponents) and mandate proportional division of delegates in all states (so that Jackson can no longer be shut out by winner-take-all rules in places like Pennsylvania and California.) Galston and Maslin independently predict that Jackson could win at least 35-40 percent of the delegates under the new rules. And that could create an agonizing dilemma. In Galston's view, nominating Jackson "would saddle the Democratic Party with an ideologically coherent program well to the left of any in modern times and have very, very serious effects down the ticket . . . ." On the other hand, Maslin pointed out, "Democrats may face a situation where the only basis for denying him {Jackson} the nomination is his race . . . . If he were denied again . . . it's possible George Bush could get 20 percent of the black vote," nearly doubling Reagan's share. It is that prospect which adds a sharp political point to the announced strategy of aggressive "outreach" to blacks and other minorities, proclaimed last week by Bush and his former campaign manager, Lee Atwater, the new chairman of the Republican National Committee. Atwater's mentor, Sen. Strom Thurmond (R-S.C.), was a symbol and beneficiary of the white backlash that drove millions, including Thurmond, out of the Democratic Party and into the GOP. But now, Atwater said in an interview, "minority outreach is my command focus, and I'm going to insist it drive my daily schedule." Through appointments to administration jobs and party posts, Atwater hopes to spur the creation of "an alternative leadership structure" in black communities. "Affirmative action has worked, and there's now a much larger black middle class," he said. Pointing to surveys showing weaker Democratic identification among young, better-educated blacks, Atwater said, "The time is right for us to reach out to them." Unstated by Atwater but acknowledged by other GOP operatives is the fact that the "outreach" strategy could not have worked with Ronald Reagan in the White House and the Justice Department leading the battle against civil rights rulings obtained under previous Democratic administrations. In contrast, Bush and his wife Barbara have made a number of gestures of outreach to blacks. For example, she insisted she wanted a black press secretary and kept the job open until she found Anna Perez to take it. Bush personally recruited Dr. Louis Sullivan, an educator/physician friend of his wife's, as secretary of Health and Human Services and held to the choice even in the face of pressure from anti-abortion groups. Bush and Atwater both used the celebration of Martin Luther King Jr.'s, birthday last week to send a signal of the change of tone from Reagan. Bush told a gathering of black Republicans that King's battle against bigotry and inequality "will, I promise, be my mission as president of the United States." Atwater, for his part, attended services at Atlanta's Ebenezer Baptist Church and said, from the pulpit where King preached, that he had missed the significance of the civil rights movement as a white teen-ager growing up in South Carolina. "But I know now," he said. With Jesse Jackson raising the stakes inside the Democratic Party, the effort by Bush and Atwater to regain a significant share of minority votes for the GOP adds another intriguing dimension to the politics of 1992.