The Australian government has been forced to declare a moratorium on oil drilling on one of the world's natural wonders, the Great Barrier Reef.

Announcing the moratorium Monday, Prime Minister Malcolm Fraser said there would be no further renewal of oil exploration permits until completion of "long-term research" on the effects of drilling.

Fraser's announcement ended a high-pressure campaign by the opposition Labor Party over the past three weeks, during which a series of leaked ministerial letters and tape recordings left the government's credibility on the reef controversy at rock bottom.

The letters revealed that despite government assurances nothing would be done to damage the reef, some ministers had secret talks with a number of U.S.-based multinational oil companies about allowing drilling to go head.

The barrier reef is spectacular area of unique coral reefs and marine life roughly the size of England stretching almost the entire length of the northern Queensland coast to Papua-New Guinea.

Lately, however, the main threat has come from the state government of Queensland led by the Joh Bjelke-Petersen, a politician who has been reluctant to allow conservation to stand in the way of developing his state's abundant natural resources. Recently he ended a campaign to save Brisbane's last grand 19th century hotel by sending in bulldozers at midnight to demolish it so a skyscraper can be built.

No one knows how much oil, if any, is under the reef's waters, but Bjelke-Petersen had been pressuring the federal government in Canberra to renew exploration permits suspended in 1971 when a royal commission was set up to examine the environmental implications of drilling.

In 1975, Gough Whitlam's Labor government established the Barrier Reef Authority, to safeguard the reef's interests. It recently recommended that a large section of the reef be declared a park. But the area contains three of the foreign drilling leases, and the Fraser government immediately intervened to delay the declaration. CAPTION: Map, no caption, By Bethann Thornburgh for The Washington Post