When the security of our nation is at stake . . . when the lives and safety of 50 decent Americans being held hostage are at stake, we want our president . . . working around the clock to protect this nation.

-- Vice President Mondale, in Iowa last Friday, defending the president's withdrawal from the Iowa debate.

Shortly after 10 p.m. on a recent Saturday, Dominic Baranello was called away from his television set when President Carter telephoned his Long Island home to do a little campaign politicking.

Carter was seeking reelection support from Baranello, the New York State Democratic Party chairman -- one of a number of uncommitted officials Carter was telephoning.

Baranello told the president he intended to remain uncommitted, but he did offer a good TV-watching tip. The chairman told the president that he had just been watching the United Nations Security Council deliberations on Iran.

"The president said he hoped to turn it on and watch it, too, in a little while," Baranello recalled. "Then he said goodbye and hung up . . . And I assume he picked up the phone and called the next guy."

So goes the newly modified campaign strategy. President Carter has been burdened by the crises of Iran and Afghanistan, and he has benefited from a dramatic rise in the public opinion polls due in large part to his efforts to deal with the crises. Now Carter has tailored his campaign to fit his needs.

He has now adopted for himself the very traditional incumbent's strategy that has long served officeholders.

A week ago, when Carter pulled out of the Iowa debate that was scheduled for tomorrow night, press secretary Jody Powell said: "The president thinks it important to maintain a posture of not being involved in campaigning actively on his behalf when he is trying to maintain bipartisan support for his policies in Iran."

But Carter's top political advisers conceded in interviews last week that the president is actively campaigning, in the way that now suits him -- and his country -- best. "The president is not shackled," said Robert Strauss, Carter's reelection campaign chairman. ". . . He is campaigning like an incumbent, and that's just the way he should be doing it.

"It's the best politics to be on the job, and using the White House . . .

This is nothing new. I've run against the White House before and I've run with it -- and with it is best."

In the two weeks remaining until the first political 1980 presidential contest that counts, the Iowa caucuses, the Carter campaign will be in high gear even as the candidate remains in the White House while his opponents, Sen. Edward M. Kennedy and Gov. Edmund G. Brown Jr., stump the state.

The Carter campaign features:

A half-hour paid television commercial which will be shown on the ABC network tonight at a cost of $86,000.

A series of TV ads on Iowa stations, lasting 30 seconds, 60 seconds, and five minutes. The five-minute ad ends with an announcer's declaration: "Carter -- it's a question of values."

A battalion of surrogates. Rosalynn and Chip Carter and Ruth Carter Stapleton and the secretaries of agriculture, transportation, labor and education will be criss crossing Iowa in the next two weeks.

And phone calls from the president.

Often the president places 20 calls a night. There have been calls of thanks to committed supporters, calls asking support from uncommitted local figures. And there have been "speaker" calls, in which the Carter agents in Iowa assemble what they call "clusters" of a dozen or so Carter supporters in a home or office or meeting hall, so that the president can call in and make a few remarks and answer a few questions.

"The idea is to find some way of keeping enthusiasm high among our supporters even though we are not going to have the candidate personally in the state," said campaign manager Tim Kraft. Keeping enthusiasm high among supporters is perhaps the key ingredient to winning in a caucus state, where voters have to be interested enough to come out and sit through a long caucus meeting on voting night.

Nineteen Democrats were gathered in the city hall of tiny Enita, Iowa, (pop. 1,100) last Thursday when the president called. They did not have a speaker phone, so they just passed the phone from person to person, with Carter talking to each of them. There were questions about inflation and Iran, but when Rodney Rogers asked about the problem of low-income housing for the elderly in Enita, the president cut him off -- he explained that he was expecting a call from the pope.

But it is the nature of campaigning, Iowa style, that Rogers got another crack at the president three days later. Carter phoned a meeting in nearby Atlantic, Iowa, and Rogers was there, and this time the president promised he would have someone personally come to Enita to look into the situation.

On another call from the president, James Leonardi, president of a postal union local in Des Moines, complained that "I have some ways we could save a lot of money in the postal service and speed up deliveries" but that he could not get to any of the "important people in Washington." Carter promised to have his domestic policy chief Stuart Eizenstat call him.

The Carter campaign style has always been a mix of policy and personality, often with the emphasis on the latter. And now the Carters are proving that the candidate does not have to be on the scene for that personal touch to be felt. In New Hampshire recently, Rosalynn Carter was talking in Salem with a Democratic organizer, Shelia Murray, who had been invited to a large briefing at the White House but had been unable to attend.

"Well, if you're ever in Washington, please give us a call," Mrs. Carter replied -- "and I'd like to have you stay at the White House."

Murray and her husband, Michael, who related the incident, were stunned at the time. Now, he said, they think they'll go to Washington in March, and they are looking forward to spending the night in the third floor family quarters.

As Tim Kraft sees it, the telephone calls and the personal-touch campaigning have "a tremendous ripple effect." Another political adviser noted that the embrace of the traditional incumbent's posture was possible mainly because Carter has come back strongly in the polls. "The front-runner traditionally tries not to be dragged into the give-and-take," he said. "Ronald Reagan is doing that now against the Republicans -- and it is working. Gerald Ford made up 32 points against us in 1976 with his Rose Garden strategy -- and we complained then, but it was effective."

Now this president's opponents are complaining about his decision not to debate in Iowa, while he is still campaigning in the semiprivacy of his telephone parlor. It is what Strauss calls "using the White House."

Yet there are times when incumbents find that they have no recourse but to risk political harm. And this came home hard to some senior aides Thursday morning, in their daily meeting with the president.

Carter made clear he had decided to reduce grain sales to the Soviets in response to their occupation of Afghanistan, and he began issuing requests for statistics on total production and economic impact. Eizenstat shook his head, according to a source who was there, and said, "We want to get you an assessment of all of the consequences of this" -- referring to the obvious political consequences of angering Iowa farmers just before the caucuses. But Carter is said to have cut him off by saying, "I don't want to debate the subject any more."

At 9 p.m. Friday, the president sat in the Oval Office and announced to the nation his decision to cut grain sales to the Soviets. Shortly afterward he telephoned a cluster in the Iowa Falls home of Carter-man Bertrand Brown, and politicked for reelection.

EPILOGUE: Last fall, when Carter was trailing Kennedy 2 to 1 in the polls, the president's political advisers gathered at Camp David. They concluded that the president was the underdog -- almost in the role of challenger -- and that he would probably have to try to force Kennedy into debating in order to gain political ground.

The Des Moines Register and Tribune decision to force a debate made that unnecessary, and Carter crisis-aided poll-vault may well have made such a debate politically unwise. Carter's top political advisers all insist that they really wanted him to go through with the debate, and that he ruled against them for foreign policy reasons. But when they were asked if they believed Carter would have canceled the debates, crisis or no crisis, if he were still down 2 to 1 in the polls, the Carter advisers paused, pondered, and said frankly they just did not know.