Johannesburg — There were jokes about a ''dads' army'' last year when the South African Defense Force got greatly expanded powers to conscript more and older men. Today the grim reality of the plan has been driven home with a call for registration of white males up to age 55 for possible part-time service in northern Natal Province - one of South Africa's most insurgency-prone areas.
The expanded call-up system is just the latest component in a drive begun some 20 years ago by South Africa to achieve a virtually unchallengeable military position against any likely threat to its white-minority government.
In large measure, this has been achieved, say Defense Force officials, military analysts, and armaments industry officials interviewed by The Christian Science Monitor.
The ''costs'' along the way have been a huge devotion of financial resources to building a large domestic weapons industry, a mobilization of white manpower that can probably go no further without damaging the civilian economy, and the strong influence national security concerns have come to hold over almost every political decision made in this country.
Rather than producing a backlash, the ongoing ''militarization'' of the South African society appears to have the support of most whites. A recent opinion survey showed a decidedly hawkish attitude among whites - in some respects even more so than that held by the government - regarding how to deal with hostile neighboring black states and the rising internal guerrilla campaign.
One of South Africa's most noteworthy achievements has been the development virtually from scratch of an armaments industry that is widely believed to be 10 th largest in the world. This has taken place mostly since 1961, when South Africa lost the security umbrella provided by membership in the British Commonwealth. That was followed by a United Nations arms embargo against the republic.
The embargo, which became mandatory in 1977, stems from international condemnation of South Africa's racial policies.
But South Africa is now largely self-sufficient in arms, most experts say, the outstanding exceptions being inability to produce locally the supersonic fighters, reconnaissance aircraft, helicopters, and ships needed by the Navy.
In fact, South Africa's armaments industry has become so large that there is a well-publicized push under way to gain export markets. The government's munitions manufacturer, the Armaments Corporation of South Africa (Armscor), says it wants to increase foreign sales 15-fold, from the current $10 million annually.
It is largely a matter of economic necessity, made more pressing by South Africa's recession. An Armscor official says: ''We gave birth to an arms industry, and this baby is going to eat us up'' unless it can be fed with export revenues.
Nations of middle and northern Africa - despite their political opposition to Pretoria - are seen as likely candidates by Armscor for weapons sales. Also, Armscor is aiming for sales in South America, the Middle East, and the Far East.
The Ratel infantry combat vehicle is seen by Armscor as having perhaps the greatest export potential. The six-wheel vehicle can carry 11 men into combat and is ''battle tested'' from experience in the Namibian war. South Africa is known to have sold some Ratels to Morocco.
South Africa has more recently developed a prototype ''go-mobile'' artillery unit it hopes will be attractive to foreign buyers. It is a quick, highly mobile vehicle with what Armscor claims is the world's longest-range gun. South Africa hopes to have the go-mobile in full production in three or four years.
Behind South Africa's growing prowess and independence in weapons hardware is the possibility Pretoria could assemble, if need be, nuclear weapons.
Aside from building a formidable weapons industry, South Africa's military planners have in recent years gained more influence in government decisionmaking , say informed military analysts. It is part of the Defense Force's ''total national strategy,'' which encourages the government to view most all matters - whether economic, social or political - through the prism of how they will affect the security and the survival of the government.
''The civilian side had no oversight of national security. The military brought this awareness home,'' says one source with close ties to the Defense Force. This source says the heightened attention to the security implications of most all government policies stems largely from the rise to prime minister of Pieter W. Botha, formerly minister of defense.
Security concerns and the survival of the dominant position of whites in South Africa are never far behind in Mr. Botha's calls for domestic ''reform.'' The theme has been hammered home in the current campaign to introduce limited ''power sharing'' with Coloreds (persons of mixed-race descent) and Indians.
Mr. Botha has often said the government could not ask these groups to help defend the republic while denying them any say in the central government.
The Defense Force is closely watching the power-sharing plans and thinking about the possibility of mandatory service for Coloreds and Indians.
''Depending on the constitutional development, you may find that in the future we will be drawing in other population groups (than whites),'' says Lt. Gen. R.F. Holtzhausen, chief of staff personnel for the South African Defense Force.
The new call-up system has already increased the burden of military service on whites. The system increases by about 50 percent the white manpower pool that the Defense Force can call on for service.
The mandatory two-year service required of all white male South Africans has not been changed. But subsequent part-time service has been significantly increased. After the first two years of service, all men now must participate in a part-time citizen force for 12 years, compared with eight years previously. Also, after leaving the citizen force, whites up to age 55 can now be required to serve in local commando units for 12 days each year.
The design of the new call-up system points to the government's conviction that its greatest immediate security threat comes from the mounting guerrilla insurgency campaign.
Commando forces are meant to act as a first line of defense, equipping rural whites to combat the infiltration of black nationalists from neighboring states.