The last has not been heard from President Carter on the subject of Ronald Reagan and the risk of war.

"It's a legitimate issue," White House press secretary Jody Powell said last week after the controversy over Carter's assertion that the November election "will determine . . . whether we have peace or war."

In fact, Carter political strategists view "war and peace" not just as a legitimate issue but as "the issue" of the campaign, and the president is likely to return to it repeatedly between now and Nov. 4 no matter how much criticism he receives for waging a "mean" and "low road" campaign against his Republican opponent.

"You don't relent, you don't stop, you don't get scared because a bunch of editorial writers say Jimmy Carter is being mean again," one Carter strategists said.

There are at least two risks to this strategy. One is that in the process of trying to portray Reagan as a Warmonger," Carter will indulge his habit of overstatement seriously damaging what is generally considered his greatest political strength -- his reputation as a decent man.

Moreover, rising the "war and peace" issue has given Reagan and the Republicans the opportunity to counter with attacks on the president's "weak and vacillating" foreign policy and to charge that this and what they say has been a decline in American military power under Carter pose the more serious threat to peace.

Thus last week, with the fighting between Iran and Iraq forming the backdrop, Carter urged calm and evenhandedness while Reagan asserted that the administration was at least partially responsible for the conflict because of its policies toward the former shah of Iran.

The president is willing to risk criticism of his campaign tactics because his drive for reelection is based on a single premise: that if public doubts about Reagan's personal qualifications for the presidency can be reinforced, the GOP nominee is a sure loser on election day.

Patrick Caddell, the Carter campaign pollster, calls this the "acceptability barrier" that must be overcome by any challenger to an incumbent president. The challenger's first task, Caddell urges, is to make the public comfortable with the idea of him sitting in the Oval Office.

In 1978, Carter, a one-term governor of a Deep South state whose constant talk of "love" and religion made large segments of the electorate uncomfortable, barely cleared that barrier in his race against President Ford. The Carter strategists' view is that Reagan's problems in making it over the same hurdle are even more serious.

According to Caddell and others, Reagan is viewed as decent and likable.

But beneath that "nice guy" image, a Carter strategists said, there are doubts about whether the Californian is "too old, with no depth, not smart enough and not hard working enough" to be president.

Operating on the assumption that these findings, produced from Caddell's polling data, are accurate, the Carter campaign has sought to exploit them in the area where they could be expected to cut deepest in political terms -- the question of war and peace. This is a prescription for negative campaigning and as a result the president at times has appeared literally to be trying to frighten the American people out of voting for his opponent.

For example:

In his acceptance speech at the Democratic National Convention last month, Carter said, "The life of every human being on earth can depend on the experience and judgment and vigilance of the person in the Oval Office. The president's power for building and his power for destruction are awesome. And the power is greatest exactly where the stakes are highest -- in matters of war and peace."

Opening his campaign on Labor Day is Tuscumbia, Ala., the president blended an appeal to southern chauvinism with the same "war and peace" issue. " . . . In all our nation's wars, young men from the South have led the rolls of volunteers and also the rolls of casualties. We southerners believe in the nobility of courage on the battlefield. And because we understand the costs of war, we also believe in the nobility of peace."

The next day, at a "town meeting" in Independence, Mo., Carter accused Reagan of planning to set off "a massive nuclear arms race against the Soviet Union" that would pose a "serious threat" to the "safety and the security and the peace of our nation and of the world." He also suggested that Reagan did not "believe in peace."

Then last Monday, in a speech to the California AFL-CIO, the president took the issue one final step. He dropped all qualifying language to say the election will determine "whether we have peace or war."

Reagan called Carter's assertion "beneath decency," and Powell conceded it had been an "overstatement," but neither Powell nor other White House aides showed any remorse.

Rather, they seized on the incident to continue their effort to plant public doubts about Reagan as a commander in chief. At the airport in San Jose, Calif., Tuesday morning, Powell boarded the press plane and pulled from his pocket a list of previous Reagan statements Carter aides had hoped would first be used by the president during a nationally televised debate with his opponent.

The list was a series of Reagan quotations suggesting U.S. intervention in a number of international disputes and Powell could not restrain his glee as he read them over the airplane's public address system.

"Ay, yes, Cyprus," he said coming to one of the quotations.

"How about Angola," Powell said at another point. "Do you want another African country? Are we going too heavy on Africa or heavy on the Caribbean?"

"Give us Angola," the reporters answered in a chorus.

The Carter strategy, as it has been from the first, is to keep hammering at this time in the hope that the last weeks of the campaign will find Reagan on the defensive, trying to convince voters his election would not risk war. "If this becomes the central issue of the campaign, the guy [Reagan] loses big," one Carter aide said.

Powell and other Carter advisers were not satisfied with last week's results. Their carefully researched list of Reagan quotations, which they hoped would throw the GOP nominee on the defensive, was lost amid all the name-calling by the two campaigns.

But they and other Democrats will be back to it as the election nears.

Yesterday, for example, Senate Majority Leader Robert C. Byrd joined in, criticizing Reagan for "careless, wild, bellicose statements" during moments of international tension.

"Mr. Reagan fails to distinguish between a local conflict on the one hand and what is necessary for national security on the other," Byrd told his regular Saturday press conference. "His statements lead people to believe that nobody would dare fool around with the United States because under his presidency we would use force."

It is all part of the Democratic strategy designed not to vindicate Carter's presidency but to frighten the country into not voting for Ronald Reagan.