People who choose to vacation in January generally do so to escape the icy blasts of winter. They can more often than not be found heading south, to Florida or perhaps the Virgin Islands.

But not Bob Dunn, whose title is White House trip director and who is in charge of advancing presidential trips.

"He's going out of town today and won't be back until the 22nd or 23rd," Dunn's secretary said yesterday.

Where, a reporter wondered aloud, could Dunn possibly be going at this time of year?

"You don't ask and I won't say," the secretary replied, laughing.

Dunn left Washington yesterday for Iowa, where he is to remain through the Jan 21 Iowa precinct caucuses, considered the first test in the 1980 presidential campaign.

Valerie Pinson, a lobbyist on the White House congressional relations staff, is scheduled to leave for Iowa today. Landon Butler, a top deputy of White House chief of staff Hamilton Jordan and the chief presidential liaison with organized labor, was also scheduled to leave today, but had to postpone his plans because of the death of former AFL-CIO president George Meany.

Butler heads for Iowa Tuesday, immediately after the Meany funeral.

"Half this place is going to be empty next week," a presidential aide said, nodding toward the offices in the West Wing of the White House.

There is no precise count of how many White House officials are already in Iowa or scheduled to travel there next week. White House press secretary Jody Powell yesterday guessed that the number may approach two dozen by the end of next week.

"We're going to put as many people in there as we can," he said.

White House officials say all of this will be strictly on the up and up. Those government officials who will be missing from their offices next week will be on "vacation" doing what they want on their own time.

Iowa does not immediately come to mind as a favorite winter vacation mecca. At last report, the termperature in Des Moines was hovering around 10, the wind howling off the prairie.

But Iowa is where President Carter needs these aids for the next 10 days, and Iowa is where they will be.

The White House had always planned a last-minute influx of help in Iowa, where Carter faces his first test against his Democratic rivals, Sen. Edward M. Kennedy (D-Mass.) and California Gov. Edmund G. (Jerry) Brown Jr. But as the date for the caucuses has approached, White House nervousness about the outcome has grown, and the response has been to pour more bodies into the fray.

Two factors principally account for the jittery White House reaction. One is that, while the Kennedy campaign has had its troubles nationally, it is believed to be well-organized and fully staffed in Iowa. And Iowa, as a caucus state, is preeminently a test of organizational strength.

The second factor is fear of the damage done to the Carter campaign in Iowa and other farm states by the president's decision to order a partial grain embargo against the Soviet Union.

What the White House aides do in Iowa in the next 10 days will depend on the needs of the campaign and their own abilities. "I suppose I'll drop in on some of the labor folks," said Butler, who in the last three years has been dealing with union leaders across the country on behalf of the president.

The White House did much the same thing in November, when the stakes were only the outcome of nonbinding caucuses in Florida. From now until the Democratic presidential nomination is finally settled next summer, it will be standard operating procedure as White House offices are emptied before key primary contests.

"You can expect roughly the same procedure in the other states," one official said.