Printed on the white T-shirt in a shop window on Second Street here are the words, "I'm staying-How about you," with a green-colored map of Rhodesia in the center.

Probably no question is more pertinent today to the future of this country's slowly dwindling white population as the Christmas holiday approaches, schools let out and the usual mass rush abroad gets under way in earnest.

With the warr against nationalist guerrillas closing in and black rule drawing near, white Rhodesians are leaving in ever greater numbers for other lands and greener pastures. October saw a net loss of nearly 1,600 whites and the record figure for the year is expected to reach at least 12,000.

This year, the December vacation exodus has a special significance as no one is quite sure how many of the 25,000 to 30,000 Rhodesians leaving really plan to come back. Thousands of white Rhodesians had made "contingency" plans to go for good by the end of December, when black majority rule was to be ushered in.

Now, however, the elections leading to black rule have been postponed until April 20, leaving these whites wavering in their departure plans. Still, as of this month, January and February are expected to see the largest flight yet of whites, whose numbers have already dropped from a high of 278,000 in 1975 to around 250,000, according to official figures, and to 220,000 by unofficial estimates.

Some alarmists here are predicting that the white population may even drop below 200,000 by the end of February. This prediction is based on the fact that the Rhodesian Reserve Bank is reported to be processing more than 20,000 departure permits. Taking four as the average size of a family, this would seem to indicate at least 80,000 whites are planning to leave over the next sex months.

This allows a departing family to take out about $1,450 and to export up to $8,700 in personal belongings, including shipping costs.

Another indicator of the growing white flight is that moving companies are now reporting backlogs up to 2 1/2 months for shipments abroad.

That the white exodus has become a major preoccupation of the government is nowhere clearer than in Prime Minister Ian Smith's recent multiple appeals for whites to stick it out.

"It must be obvious to you all that our future success does depend on whether our whites are prepared to stay with us and play their part in the future country taht lies before us," he said in an early December televised "fireside chat." "I hope they will see it through."

The institution most affected has been the army, which depends heavily on white officers, NCOs, and reservists for its effectiveness. Not only have thousands of young whites eligible for the callup left, but also hundreds of the "professional soldiers" and foreign mercenaries who came here in the name of the white Rhodesian cause.

"I know of one high school where 24 of the 26 [seniors] are going abroad for vacation now and none are expected to come back," said one Rhodesian, explaning the attitude of many white youth toward the draft awaiting all graduates and droupouts.

The holiday season is normally the high point of travel for white Rhodesians. In addition to the usual 40 flights a week between Rhodesia and Johannesburg in South Africa, Air Rhodesia and South African airways are together putting on an extra 17 flights this month to cope with the vacation exodus.

The two airlines and travel agencies report flights are already fully booked through the first week of January, although many reservations are known to have been made on a "contingency" basis months ago. After elections were postponed to April and a penalty fee slapped on unused reservations, Air Rhodesia reported 5,000 cancellations and rebookings.

While most whites prefer to leave by airplane because of the dangerous war situation, more than 6,000 are expected to join one of the once-a-day convoys and travel by road via Beitbridge to South Africa this month.

At Christmas time, the army provides both air and ground protection for the highly vulnerable, slow moving convoys. With the line of cars and trucks stretching over three miles or more, however, the convoys are still an easy target for guerrilla attack.

One reason official emigration figures are so unreliable is that unofficial final departures are so easy. Many whites takes advantage of the vacation travel allowance, which is more generous than the departure one, just to skip the country.

The government allows about $435 per person each year for Rhodesians vacationing abroad. If a family of four has not been outside for two years, it could take out more than twice the official departure allowance.

Many white Rhodesians have been quietly scouting out places for settling down-in Australia, Europe, Latin America, Israel and the United States. Typical of the growing number of "sundden departures" after such scouting trips is Les Brener, head of the Rhodesian Pharmaceutical Association and former president of the Salisbury Chamber of Commerce. The local press reporteed this past week that he left without notice with a one-way ticket for Australia.

Not all are veiling their departure plans under business or vacation trips abroad, however. Colin and Irene Reichert, for example, have told all their friends of their intention to pick up stakes and settle outside Palm Springs, Calif., where their only son lives.

A trip to the United States last May radically changed their view about life in Rhodesia. "We were going to stay and see how things go," said Colin, a diesel mechanic, in an interview. "Then we saw the States and that was it."

"We had freedom, boy, freedom," added Irene.

Like many white Rhodesians, the Reicherts have found life here more and more confining, nerve-wracking and generally difficult as the guerrilla war steadily worsens.

"you cannot go anywhere here now," said Colin, still dressed in his army camouflage uniform having just returned for a 48-hour furlough on his latest callup. He served more than seven months last year and four this year.

"We have lived a grand life here, but it isn't such a grand life any more," said Irene, whose great-grandfather was one of the original pioneers settling Rhodesia and had the distinction of having the first tin roof on a house in the eastern border town of Umtali.

Contrary to the standard image abroad of Rhodesia as a land of colonial milk and honey, the Reicherts have calculated they will be far better off living in the United States. While the cost of living in the States is twice that here, Colin said he will be earning four times as much.

The Reicherts were also struck by the availability and cheapness of things generally in the United States compared to Hodesia. "If a car breaks down here, you don't even know if you are going to get spares," Colin remarked.

The Reicherts have just sold their $25,000 home in an all-white suburb of Salisbury and are anxiously awaiting word from the U.S. Embassy in Pretoria, South Africa, which handles all Rhodesian immigration requests. "As soon as we get our visas,"we will go," said Irene. "We are just taking three suitcases and 1,000 bucks."