After waging war for months against candidates they oppose, antibortionists are mounting a coordinated effort in support of Ronald Reagan, the most outspoken abortion foe of the remaining presidential hopefuls.

As the probability has grown that Reagan will win the Republican presidential nomination, the anti-abortion movement has spread the word that Democrats should vote for him against either President Carter or Sen. Edward M. Kennedy in November.

Should it catch on, such a drive could play a key role in the election. Opinion polls suggest that most antiabortion activists are Democrats, and that many of them consider the abortion question more important than party labels.

Voter surveys after the April 1 Wisconsin primary -- which resembled a general election in that voters could choose a candidate from either party -- showed that Reagan won votes from Democrats and independents because of his anti-abortion stand.

In the 1976 election, the first presidential race since opposition to abortion emerged as an important political force, anti-abortion activists had no strong perference because both Carter and President Ford opposed a constitutional amendment to ban abortions. Support of such an amendment is the political test for anti-abortionists.

Carter remains opposed to a constitutional amendment. Reagan strongly supports the idea and has even backed proposals to force a constitutional convention if Congress refuses to propose such an amendment. In his campaign speeches, Reagan has promised to use the power and prestige of the presidency to push for an amendment if he is elected.

His position has won Reagan the support of most anti-abortion groups nation-wide, giving him a built-in corpsof highly motivated activists in every state.

There is really no single anti-abortion "movement;" the political force is a not-always-harmonious consortium of groups bearing such names as "Citizens Concerned for Life" (Minnesota), "The Pro-Life Party Inc." (New York and other states), "Americans forCatholic Values" (New Hampshire), and "Iowa for Life."

The organizations have their differences over substance -- including the question of whether abortion should be permitted to save a woman's life -- and tactics -- including a continuing dispute between people who maintain allegiance to the major parties and those who prefer an independent political effort.

But interviews with about 300 antiabortion workers in 27 states over the past six months show a consensus on basic points.

The people who turn out to demonstrate against abortion in a downpour at dawn or wait in the cold for hours to shout their cause at candidates and reporters all believe that they represent a growing political force, and that the 1980 presidential campaign is their chance to prove it.

In the first months of the campaign they tried to do this mainly by demonstrating against candidates they opposed.Kennedy was the chief target, even though there is no difference between him and Carter on the question of an anti-abortion amendment.

Kennedy earned the ire, and in some cases, the evident hatred of antiabortionists partly because of his long record of Senate votes in favor of Medicaid funding for abortions. And he was the target partly because, as Madeline Appleby, who picketed outsidea Kennedy rally in Littleton, N.H. -- put it: "He's a Catholic and he ought to know better."

"As for the Dems," noted the antiabortion newsletter "Lifeletter" in a recent survey of the presidential race, "well, it's obvious that anti-abortionists want bogeyman Ted not just down but out before they start blasting President Carter's lousy abortion record."

But other candidates, too, drew demonstrations. Carter's surrogate campaigners have been targets, as has George Bush. John B. Anderson, the only candidate who argues agressively inhis speeches for a woman's "right" to choose abortion, has begun to run into demonstrations at most campaign stops.

In recent weeks, however, opponents of abortion seem to have shifted gears. The tone of their political effort has switched from predominantly "anti" various candidates to a heavily pro-Reagan campaign.

Among those working to steer anti-abortionists around the nation onto the pro-Reagan course are such recognized leaders as Nellie Gray, who leads the "March For Life" in Washington each spring, Paul Brown, chairman of the Washington-based Life Amendment Political Action Committee, and James McFadden, who heads the New York-based Ad Hoc Committee in Defense of Life and edits Lifeletter, which seemsto be the most widely read anti-abortion publication.

Some anti-abortionists, however, who have not yet agreed that support for Reagan in November is an acceptable course. A leader of this faction is Ellen McCormack, who ran for the Democratic presidential nomination in 1976 on a "pro-life" platform and is running again this year as an independent. 1

McCormacks Pro-Life Party took out blistering newspaper ads during the New Hampshire and Illinois primaries noting that Reagan, as governor of California, had signed at 1967 state law that considerably liberalized the right to obtain an abortion in that state.

Until 1967, California law forbade abortions except when a woman's life was threatened. The law Reagan signedalso permitted abortions when a woman's physical or mental health was jeopardized, and in cases of rape or incest. The statute was rendered moot by a Supreme Court ruling in 1973 that voided most state laws against abortion.

Reagan now says, as he did in 1967, that he had serious doubts about the statute but signed it because he felt some change was necessary in California's previous law.

The McCormack faction also disapproves of Reagan's promise to support Republican congressional cndidates who will not take the total anti-abortion pledge.

But this "purist" view of Reagan seems to be declining among abortion opponents as McCormack has discovered in her independent campaign for the presidency.

"People who were for us in 1976 now say, 'Well, Reagan isn't perfect, but he's electable,'" complains Linda Zumpano, manager of the McCormack-for-President campaign.

"We get a lot of feeling," Zumpano adds, "that Ellen (McCormack) is somehow muddying the waters, you know, that everyone who is supposedly right-to-life should get united behind Reagan so our side can have a winner."