100 percent self-sufficiency in oil?

Oil and gas exploration in Australia has had what one industry official calls a ''new lease on life'' these past few years, despite a big, soft world supply cushion and static or declining real prices.

The federal Bureau of Mineral Resources (BMR) has just released an upbeat new forecast of the country's oil and gas self-sufficiency.

But exploration would be severely cramped, and that self-sufficiency impaired , many in the oil industry insist, if the government went ahead and imposed a new resource rent tax.

The new BMR study projects oil and gas self-sufficiency, now at 65 to 70 percent, to go to 90 percent by the end of the 1980s, with production almost equal to demand by the early 1990s.

''You have to distinguish between absolute self-sufficiency and technical self-sufficiency,'' explains Sen. Peter Walsh, the federal minister for energy and resources. Australia has a lot of oil, but it's very light crude - ''motor spirits.'' Even if the country produces enough to export, it will still import to meet its needs on the heavier end of the oil spectrum: fuel oils and the like.

Some private sources (notably Esso Australia, which has become the unofficial forecaster among Australia's oil companies) have criticized the BMR assessment as too rosy, at least short term.

The Broken Hill Proprietary Company Ltd.'s newly discovered Jabiru 1A well in the Timor Sea has been a significant factor in the BMR assessment. But Brian T. Loton, BHP's managing director, holds both the BMR and the Esso Australia estimates somewhat at arm's length.

''It's very difficult to foretell the future, isn't it?'' he says with a confidential smile. But he reaffirms BHP's opposition to further taxes. ''We think the crude oil pricing policy, which was introduced by a Labor government in 1975, has been responsible for finding more oil, and for increasing our oil self-sufficiency. This policy said that new oil would attract full world price and the producers would be subject only to the normal taxation regime, plus a royalty - which recognizes that this is a nonrenewable resource. The resource rent tax is to be an additional tax on top of that.''

John MacLeod, chief economist at CRA Ltd. in Melbourne, argues that the new tax makes some unrealistic assumptions. If the return isn't high enough - and the tax would be another cut into that return - explorers won't explore. ''Every explorer wants a bonanza. He doesn't want a savings bank rate; he doesn't want a bond rate.''

Senator Walsh, though, has called the ads used in the oil industry campaign against the tax ''at best simplistic and at worst dishonest.''

The resource rent tax, Mr. MacLeod says, ''is on a losing streak at the moment, but I'm sure it's not dead.''