At a recent cocktail party in Johannesburg white Parkton suburb, a small group of young South Africans clustered around two American guests, firing questions:

"How do we get into the States?" a teacher queried.

"Do you have to get a guaranteed job first? Or can you go over on a juorist visa, find a job, and stay?" and accountant asked.

"Where's the best job market?" an engineer asked anxiously.

A few days later, a South African photographer invited an American colleague to join him at a local pub to discuss "something urgent." The subject: How he and his wife could emigrate to the United States.

The encounters reflect a growing trend in South Africa: the rethinking of whites about their future here. It started after racial unrest erupted in mid-1976 and went on sporadically for the rest of the year.

Statistics reveal that more than 15,000 persons decided to emigrate last year. This constitutes the greatest exodus from South Africa since 1961, when the country experienced its first modern racial unrest at Sharpeville.

Only recently, however, has it become clear just who is leaving and what the impact of their decision - politically, economically and psyschologically - will be on a country where blacks outnumber whites by more than four to one.

From the few figures available, it appears that it is mainly young professionals and families of Jewish descent who are leaving.

South African emmigration to Israel is increased by 28 per cent last year, according to officials here. About 700 persons registered to go to Israel in the first six months of his year.

A Washington lawyer who has been to South Africa twice recently said he has been flooded with Jewish clients seeking help on ways to emmigrate.

It is now common to see headlines in local papers declaring: "A Massive Brain Drain of Professionals Fleeting the Country" or "Planeloads of South African Doctors Heading for the U.S."

A 1976 graduate of the University of Witwatersrand business school claimed that more than half of his peers made inquiries about jobs abroad to enable them to leave South Africa permanently. Those who did not land jobs outside the country were still looking while holding temporary jobs here, he added.

Earlier this year The Johannesburg Star reported that a planeload of more than 200 South African doctors flew to the United States to beat a Jan. 9 deadline, after which doctors from other countries must take examinations before they can register to practice without restrictions.

A Jewish gynecologist explained, "I would rather stay in South Africa. But, of course, we are all worried about our future here. Most of my colleagues have started making contingency plans."

Lawyers in Johannesburg who handle emigration cases say professionals and Jewish families dominate the figures for one or more of three reasons: Marketable professional skills, foreign passports, or sufficient funds.

Most governments now have immigration requirements that include one or a combination of qualifications such as skilled training in vital job areas or a minimum of several thousand dollars in available funds or investments.

Foreign passports also provide a means of emigrating. This is especially true among English-speaking South Africans who can trace their English ancestry and apply for British passports, or Jews, who are automatically for Israeli citizenship.

British consulate officials here say there has been a significant increase in South Africans applying for British passports. The flood of inquiries is continuing despite the current lull in racial disorders, although no figures are available.

"I would guess they're either planning to move or taking out insurance against the time they need to have their documents in order," a consular official explained.

British passports have become such popular possessions that last month police uncovered an elaborate $2 million smuggling opertion in Johannesburg involving the printing of thousands of forged British passports.

The loss of this class of South Africans will have a major impact on the troubled territory, where there is already a shortage of skilled personnel. For years, the South African government has sponsored a massive campaign to attract white immigrants. Last year, more than 43,000 came to South Africa, according to government statistics, giving the republic a net gain of more than 30,000.

Diplomatic sources indicate, however, that a large percentage of the emigrants were white Rhodesians and Portuguese from Mozambique and Angola, often with few funds or low priority skills.

The loss of young professionals and Jewish entrepreneurs will have an impact on South Africa's already-troubled economy, robbing it of the personnel it needs the most, and starting a snowball effect on other businessmen and professionals said a financial journalists who plans to leave the country soon.

The increase in emigration has also led to a new problem: currency violations. Both those leaving and those thinking about leaving attempt to buy foreign currency illegally to cover the expenses of rebasing and to meet the requirements of foreign governments.

Because of a serious balance-of-payments problem, South Africa has strict laws about funds emigrants can take with them: the equivalent of $11,600 for a single person, and ajust under $35,000 for a family. In most cases, this is not enough to meet the immigration requirements of the most popular foreign countries, the United States, Canada, Britain and Australia.

Black market negotiations have started. An American visitor claimed he was offered a "one-to-one rate by four different shopowners or salesmen in a 10-day period. The legal rate is about one South African rand to $1.16 cents.

Several tellers at the airport branch of the Volkskas Bank were recently charged with under-the-table foreign exchange deals - selling foreign currency in excess of the legal limit. This was particularly embarrassing to the government, which is one of Volkskas major clients.

Based on the growing number of inquiries at local consulates, diplomatic sources are convinced that the emigration trend will increase.

As one Western official explained, "It seems that people here don't want to talk about anything else. Last year the topic was whether whites had a future here. Now it seems many have decided, at least according to numbers who are applying for resident permits."

Government officials have already conceded that the available figures may not reflect the real total. "We are aware that not all those leaving South Africa state that they are emigrating," one official said in February.

Minister of Interior Connie Mulder argues that the recent loss is not serious: "It is quite understandable that when circumstances become difficult people run away. The man who can move easily will simply leave rather than face these challenges. I would say: the sooner he goes, the better."

Mulder added: "It does not disturb us at all if they leave. It is just Africa selecting its own sons, those who have the backbone to stand up to the challenges of this beautiful continent. There is no reason for panic. I still sit here and daily receive requests from people who want to come to this country but cannot do so because of our stringent requirements."