Jimmy Carter's singular quality as a political animal lies in an uncanny ability to sniff a rival's weakness and expose it to public view. By that means he has already -- in his 1976 campaign and his bid for reelection this year -- compiled a formidable list of the most diverse victims.

Abundant signs now show that Carter is on the move against Ronald Reagan. Reagan is also likely to go down unless he shows a good deal more acumen -- particularly in picking a running mate -- than he has demonstrated so far.

The first victim of the Carter tactics was George Wallace. Wallace's weakness was the "never" view on desegregation. Carter picked a semi-southern state, Florida, and came on, from his favorite position of underdog, as a man of the New South. Wallace hasn't been heard from since.

Sen. Harry Jackson of Washington, despite manifold virtures, bore the stigmata of the Old Politics associated with the big city Democratic bosses. Carter, appearing as the paladin of New Style participatory politics, looked good in Iowa and New Hampshire, and in Pennsylvania drove Jackson back to the Senate.

Rep. Morris Udall of Arizona was a campus liberal, in the mold of Adlai Stevenson. Carter ran against him as the good old boy from the rural South and finished him in the southern-most of the northern states, Ohio.

With nobody to profile his protean self against, Carter slumped badly after the 1976 primaries. But he had the delegates and he started the president campaign with a huge lead.

Perhaps because President Ford was behind, he proved to very tough for Carter. Only when Ford drew abreast in the last few weeks did Carter identify his weakness -- anti-poor-people Republicanism. In the end, Carter beat Ford in Texas by appealing, in LBJ style, to the Baptists of the piney woods, the blacks of Houston and the Hispanics of the valley.

Ted Kennedy was the next to go. The chink in his armor was a personal life summed up in Chappaquiddick. Carter not only raised questions in direct advertising about Kennedy's trustworthiness. He also gathered the mantle of office about his person in the White House to show himself as a grave statesman, a veritable Cato of concern about Iran and Afghanistan. By not venturing forth on the frivolous business of campaigning, he smashed the image of Kennedy invincibility.

Reagan's flaws abound. He has no experience in national or international affairs. Most of his life he has been an actor. He has close ties with the right-wing ideologues of the Republican Party. So to discredit him, it suffices to identify him in the mind's eye of the voter as an irresponsible figure, prone to go off half-cocked on such tricky matters as arm control and taxes, and certainly not to be trusted with final management of peace and prosperity.

The administration's record, to be sure, presents something of a handicap to Carter. During his tenure at the White House, inflation has soared and recession has come round again with a vengeance. There has been a notable drop in the country's influence abroad -- to the point where the French and Germans have apparently decided to manage alliance policies toward Russia, the Middle East and the Persian Gulf.

Given those conditions, Carter has performed near-miracles. He is on the vege of accepting a tac reduction to stimulate the economy he forced into recession. But he is going for discriminating cuts that will reflect badly on Congress or any opponent unwise enough to favor meat-ax proposals.

At meetings with foreign statesmen in Europe two weeks ago and more recently in Japan, he made news, and kept the kind of company presidents are supposed to keep. To protect himself against charges of softness, he affected a suspicious attitude toward French and German proposals for dealing with the Russians. But he has allowed himself to drift toward negotiations with Moscows as the Man of Peace.

Foiling these tactics requires only a candidate able to lay out a sound policy and then go after the Carter record. Reagan, in the choice of a vice president, has a particularly juicy opportunity to show he is not irresponsible. By picking Sen. Howard Baker or former ambassador George Bush, he would demonstrate beyond cavil sound common sense and a willingness to look quality in formulating domestic and foreign policy.

But so far, anyhow, Reagan seems not to know his own mind. He has allowed the vice presidential choice to become a speculative free-for-all. He has let senators and congressmen push him into a position on arms control that looks positively dangerous and a tax cut that can be labeled unreliable. The more so as Reagan's failure to release his tax returns is bound to raise public suspicion that he has a personal problem.

If Reagan continues to let his followers push him around, he will not be able to hold the slight lead he now enjoys. Nor will he deserve to.