Vietnam. It's still a sensitive issue for many Americans. Now Gary Hart is trying to inject Vietnam, and its bitter lessons, into the 1984 Democratic race for the White House.
Already, Senator Hart's new ploy has sent the sparks flying.
In full-page newspaper ads this week, Mr. Hart charges that Walter Mondale has failed to learn from the history of America's experience in Vietnam. He claims that Mr. Mondale has sided with President Reagan on the use of force in American foreign policy.
Mondale retorts that Hart's policies are ''naive.'' He suggests that Hart would fail to cooperate with America's allies to preserve peace around the world.
The salvos over foreign policy are expected to escalate as Hart and Mondale square off in the pivotal New York State primary next week. New York (285 delegates) will be the biggest Democratic prize this year except for the June primary in California (345 delegates).
The foreign policy attack by Hart is part of a new strategy to put Mondale on the defensive. The Hart staff also wants to turn media attention toward the issues and away from recent examinations of Hart's personal history and life style.
Those recent stories, many of them negative, have hurt. Hart's standing in the latest CBS-New York Times poll of Democrats, for example, finds that Mondale now leads Hart 42 to 35 percent nationwide. Just two weeks ago, Hart had a seven-point lead (38 to 31) over Mondale.
In coming days, Hart's new initiatives in foreign policy will be supplemented by major speeches on both civil rights and economics. Foreign policy, however, holds the spotlight for now.
Hart's attacks on Mondale are sharp - and somewhat risky. His comparisons of Mondale and Reagan could antagonize some Democrats. Examples:
On Lebanon. ''Ronald Reagan dispatched US marines to Lebanon on a futile mission that sent more than 260 young men to their graves. Walter Mondale stood by and was mute. . . .''
On Central America. ''My proposal to withdraw (US) troops has been challenged and criticized, not by Ronald Reagaqn, but by Walter Mondale, who attacks it with language that chillingly recalls the Vietnam era.''
On Vietnam. ''While I was working with Robert Kennedy and George McGovern to end this tragic war, again, Walter Mondale stood silent. . . .''
The Hart-Mondale clash over foreign policy could be useful to voters because there do appear to be genuine differences between the two men.
The Vietnam experience seems to have colored and shaped Hart's fundamental outlook. This is true whether that policy relates to a third-world conflict, such as El Salvador, or a big-power rivalry, such as the Middle East.
There are few issues that show this more clearly than Hart's attitude toward US defense of Mideast oil. The Gulf remains a vital energy source for the free world, especially Japan and Europe.
Hart has said: ''We have to first strive for our own independence from Middle East oil, and then tell our allies, who will always need it, that they can't rely on us when things explode there.''
In practical terms, as explained by Hart's staff, his policy is this:
1. If an outside military power attempted to seize the oilfields of the Mideast, the US should first contact its allies and try to coordinate a response.
2. If Europe or Japan wished to put troops ashore to defend the oilfields, then the US would be willing to consider providing Naval support.
3. The US would not be willing to commit its ground forces in the Gulf area in defense of oil.
This policy, as explained by Hart staffers, is ''based on a broader one that seeks American energy independence.'' The best way to stay out of a war for Mideast oil is to be certain that the US doesn't need that oil for its survival.
This is one reason Hart has supported a controversial $10-a-barrel tax on imported oil. He wants to wean the US from its appetite for energy that comes from high-risk areas of the world.
Mondale reacts sharply to Hart's ideas. In a speech this month to the Chicago Council on Foreign Relations, Mondale said: ''In my judgment, my opponent has failed to think through his proposal and to weigh its consequences wisely.'' Earlier, in their debate in Atlanta, Mondale was even more blunt:
''A few days ago,'' he noted, ''Senator Hart said that if Persian Gulf oil were interrupted, that the allies would be on their own and they couldn't look to us for help. In my opinion, that is naive. All history teaches us that we must stand together as an alliance and work together for the security of the Western world.''
Mondale accuses Hart of introducing ''a strange new vision of our role in the world.'' This vision ''threatens to weaken our crucial alliances,'' he charges. The US cannot ''live in isolation,'' he says.
Hart's foreign policy strategy appears based in part on heavy reliance on sea power - a concept that has earned him the nickname ''Admiral Hart.'' Naval supremacy would provide a means, without using US ground forces, to cut off efforts by the Soviets or others against third world nations. Hart also wants to bring into play US supremacy in the fields of culture, economics, and politics, rather than rely on an essentially military approach. This idea can be seen in his attitude toward Central America, where he again disagrees with Mondale.
Hart throws down the gauntlet to the Reagan White House in Central America. He charges that the principal enemy in the region is ''not communism - it is poverty.'' He would rely primarily on economic help, less on military action.
Specifically, Hart would slash the US military presence in Central America and would halt all aid to rebels fighting the Marxist government in Nicaragua.
He charges that ''Mondale or Reagan policies'' in the region ''will see a rather large loss of American lives.''
Mondale responds that he would remove some US forces from Honduras, for example. But he would leave others in the region to encourage the withdrawal of Cuban forces based nearby.
Meanwhile, both men are vying for New York's large Jewish vote by lining up solidly beside Israel. Both say they would move the US Embassy there to Jerusalem - a step that could anger Arabs. Mondale claims Hart came late to that position, a charge Hart denies.