S. Africa tightens fetters. PRETORIA TARGETS NEW GROUPS

The South African government's crackdown on militant opponents has entered a new phase. Newly targeted are areas of public life that had been relatively unfettered by the 15-month-old state of emergency. Pretoria is trying to rein in institutions seen as ``promoting violent revolution,'' or serving the aims of the outlawed African National Congress (ANC).

Stage 1 of the campaign began this week. It involves new press curbs that allow, for the first time, pre-publication censorship (see Story, Page 32). The restrictions are aimed at newspapers deemed to be ``promoting or fanning'' a wide range of antigovernment activities. Most threatened is the so-called alternative press, made up chiefly of publications that focus on the black community.

Top officials have also signaled they intend to eliminate antigovernment militancy from two other public arenas: universities, and extraparliamentary political groups.

Despite the state of emergency, antigovernment debates and demonstrations have persisted on some campuses. And a group headed by a former white-liberal parliamentary leader recently held talks in Senegal with the ANC.

The government has indicated it is weighing the possibility of denying university subsidies - which typically covers about half of the universities' expenses - to institutions that permit such activities and to certain political organizations. The universities have reportedly rejected a proposal that would give the education minister power to withhold funding if he judges a university has failed to ``take all reasonable steps'' to curb campus militancy.

The press move has sparked a storm of protest from white-liberal parliamentarians, some academics, and local journalists. They argue the curbs will encourage rather than quell unrest, and fear they presage a general move to forcibly limit debate on the country's future. Responding to their outcry, Home Affairs Minister Stoffel Botha assured editors that the restrictions will not be applied to criticism of the government, but to incitement of ``revolution.''

The official campaign reflects the government view that its security crackdown on black political violence has not, in itself, ensured lasting stability. This, officials have come to feel, can be achieved only by rooting out political radicalism. The ultimate aim is to pave the way for talks on power sharing with moderate blacks.

The official hope seems to be that the mere threat of a clampdown - and the mere existence of new censorship powers - will cause the publications and institutions in question to curb themselves. The new censorship came only after attempts failedto get mainstream newspaper editors to rein in colleagues in the alternative press, which focuses on coverage of black political activism.

The main target of official pressure in the extraparliamentary arena is the Institute for Democratic Alternatives in South Africa (IDASA). It was founded by former liberal parliamentarian Frederik van Zyl Slabbert after he resigned his seat as opposition leader in early 1986.

Striking back at Mr. Slabbert for organizing the meeting with the ANC last month, South African President Pieter Botha threatened to limit the overseas contributions essential to IDASA and deny passports to South Africans attempting similar missions.

Central to the debate over the new curbs is a clash in fundamental assumptions about South Africa. The government believes that the past several years' unrest is the work of a radical black minority that has intimidated - partly through the news media - a ``moderate'' black community that would otherwise like to take up Pretoria's power-sharing compromise stopping short of black rule.

The government's critics argue that it has wildly underestimated the depth of support for black rule. The editor of South, a Cape Town newspaper expected to be a target of the new curbs, said last week, ``We [the alternative press] are the mouthpiece of the [nonwhite] majority in this country who have been excluded from the process of central decisionmaking.... We are trying to reflect their aspirations and wishes.''

Journalists in South Africa operate under official press restrictions.