In the trench warfare between Democratic presidential contenders competing for liberal special-interest groups, Sen. Albert Gore Jr. has made a strategic breakout that has revived his fading campaign and could transform the ideological climate of the fight for the nomination.

When Gore and the five remaining presidential candidates took the stage in Miami Oct. 5 for a debate on national security issues, the 39-year-old freshman senator's campaign was barely breathing. When he left, he had become a common target of his competitors by the simple tactic of marginally but clearly moving right on defense and foreign policy.

Democratic insiders agree Gore has scored a ten-strike. From a low base of public and party support, since Miami he has been treated by his opponents as if he were the front-runner.

His immediate motive is to keep his candidacy, which is doing poorly in Iowa and New Hampshire, alive long enough for southern-oriented Super Tuesday primaries March 8. But more broadly, he is appealing over the heads of ideologized party activists to rank-and-file Democratic voters. The real significance of the move is whether he pulls his opponents at least part of the way with him.

Gore has not gone all that far himself. He still opposes military aid to the Nicaraguan contras, which remains the litmus test on national security. He is no Scoop Jackson, or even a Sam Nunn. But he does not have to be either of these to set himself off from the field, as was shown in the Miami debate.

There, the other five Democrats persisted in ritual flailing of America's role in the world. Rep. Richard Gephardt, who is competing with Gore for moderate white southerners, suggested the United States might arm the African National Congress in its fight against the white South African regime.

How could a supposed moderate be drawn into a position where he unalterably opposes aid for anticommunist insurgents in Nicaragua and Angola but supports communist-backed insurrection in South Africa? Because Gephardt has been sensitized by ceaseless courting of party activists in Iowa and New Hampshire.

Nearly as startling was the posture of Dukakis, a neophyte on the national stage but an unmistakable McGovernite in foreign policy, suggesting this policy for the Gulf War: ''Rather than driving the Iranians into the hands of the Russians, we will back away from our support of the Iraqis or, alternatively, twist their arms to make them stop the tanker war that they started.''

Gore's response -- that ''if we had not held firm'' in the Gulf no progress would have been possible at the United Nations toward a cease-fire -- is language heard far too seldom from Democratic presidential candidates in the past five campaigns.

In many ways, Gore had seemed to be the least authentic and least prepared of the candidates.

Even his campaign manager, Fred Martin, was belittled by insiders as a wordsmith (he wrote speeches for Walter Mondale, Geraldine Ferraro and Cuomo) out of his depth politically. But Martin has devised the most imaginative tactical gambit of the plodding Democratic struggle.

Whether or not it succeeds, Al Gore has opened a door back to reality by rejecting Ann Lewis, director of Americans for Democratic Action, as arbiter for what is acceptable in the world's oldest political party. After Lewis declared Gephardt unacceptable, the Missouri congressman promptly moved left on a broad front of issues and squirmed last summer when Dukakis challenged him on past national security votes. In going the opposite way, Gore is bucking his party's 20-year quest for oblivion.