Even before the Venice summit meeting, President Carter had consigned Iran and the hostages to the back burner. Now, in the aftermath of Venice and in the light of the latest presidential election polls, it looks as if Afghanistan, like Iran, will shortly be off the White House's critical list.

For six months, Carter made the most of both Iran and Afghanistan politically, rising in the polls from a dismal low to an exhilarating high. When, however, the public became disillusioned with his handling of the Iranian problem, it disappeared from presidential view. It was barely mentioned during Carter's week abroad.

At the summit, though, Carter did make a mighty effort to revive public interest in the once-burning Afghan issue, but among our allies he met with indifferent success. And when he got back to the United States, he discovered that the home folks apparently were not impressed, either, by his recent foreign policy initiatives. A national CBS-New York Times poll, taken at the height of Carter's foreign trip, showed the president's approval rating sinking to the low 30 percent level that prevailed before sharp rise inspired by the Iran-Afghan crises.

In the past, summit gatherings, with all their pageantry and vast television coverage, have generally enhanced the popular standing of U.S. presidents. Not this time. Despite Venice and all Carter's tough talk about Afghanistan, the latest poll shows only 20 percent of the public, the smallest percentage during his presidency, now approves of his conduct of foreign policy, which has taken an increasingly hard stance during the presidential primary period.

Nevertheless, Ronald Reagan, the Republican superhawk who talks even tougher than Carter, continues to climb in the polls. The CBS-Times survey now gives him a lead of 10 to 13 points over Carter. But then Reagan has for years been a consistent hawk. He has a strong, if limited, natural constituency that feels as he does. In 1976, he almost walked off with the GOP presidential nomination by accusing Gerald Ford of being dovish.

A look at the latest polls ought to convince Carter that there's no future in trying to beat Reagan at his own game. Carter militancy, real or pseudo, will not attract Republican conservatives, but simply alienate millions of non-militant Democrats, whose votes he badly needs to win.

In this century, at least, nearly all the successful Democratic candidates for president have run in the peace mode. Woodrow Wilson won on the slogan "He Kept Us Out of War." Franklin Roosevelt won a third term by promising no American boys would be sent to fight overseas. Lyndon Johnson beat Sen. Barry Goldwater by tagging him as a "warmonger." Hubert Humphrey came within an eyelash of upsetting Richard Nixon in 1968 by a last-minute embrace of the Vietnam peace cause. In 1976, Gerald Ford might well have defeated Carter if, under pressure from Reagan, he had not abolished "detente" from his vocabulary and sidetracked his own SALT II effort, openings that Carter successfully exploited.

Reagan's hard line, like Goldwater's, may be good for his party's nomination, but it is worth noting that no outright hawk, Republican or Democrat, has ever won the presidency in modern times. Dwight Eisenhower swamped Adlai Stevenson with his I-shall-go-to-Korea" peace speeches. Richard Nixon won 49 out of 50 states in 1972 on the strength of the Vietnam withdrawal, detente with Russia and rapprochement with China. In 1968, Nixon waffled on Vietnam, but promised to get the troops out.

There's no living politician who can change course quicker than Jimmy Carter. He went to the summit to promote firmer sanctions against the Soviet Union for its Afghan aggression and to inhibit any new allied contacts or negotiations with Russia until it withdraws all of its troops from Afghanistan. He quickly perceived, however, that there was a broad and growing consensus to start talking with the Russians again (regardless of their crude Afghan mistakes) with the object of salvaging detente and resurrecting strategy arms limitations.

So when Carter left the summit, his departing words were that the meetings of French President Valery Giscard d'Estaing and West German Chancellor Helmut Schmidt with Soviet President Leonid Brezhnev could be "fruitful," even though Carter had previously frowned on such contacts.

By the time he reached Belgrade, Carter was expressing his readiness "to explore a transitional arrangement" concerning Afghanistan, combined with the pullout of "all Soviet troops" from that country. And on the flight to Madrid, officials on Carter's plane disclosed that the United States had already been quietly discussing with Russian diplomats an arrangement to end Moscow's Afghan involvement.

The joint Venice communique reasserted that the Russian occupation of Afghanistan was "unacceptable," but the NATO powers are finding that the crucial problem of East-West coexistence cannot remain at a standstill indefinitely, any more than it could after the Soviet attacks on Hungary in 1956 and Czechoslovakia in 1968.

Both those interventions were condemned by the West even more harshly than the one against Afghanistan; yet not long after the Czech crackdown, while Russian troops still occupyied that country, then-President Nixon quietly opened the negotiations with Moscow that led to his historic detente agreement with the Soviets.