By seizing the Greek tanker Manuela, bound for Beira with 16,000 tons of oil, Britain has reinforced her sanctions against Ian Smith's regime. The British drew on a resolution passed by the Security Council to put an "armed party" on the Manuela. Had the tanker reached Beira, the oil would have flowed through a pipeline controlled by the Anglo-Portuguese Lonrho Company to the Rhodesian refinery in Umtali.

The Wilson government demonstrated both restraint and forcefulness during the crisis--especially in dealing with Security Council President Moussa L. Keita of Mali when he inexcusably delayed the meeting. But it should be prepared to take broader measures if the existing sanctions do not bring Smith to his knees. Thirty thousand gallons of oil have flowed daily from South Africa during the past two months, and there is good reason to question the effectiveness of the sanctions in other areas as well.

The British are understandably reluctant to take military action against a former colony. Government officials argue that the oil from South Africa equals only about half the Rhodesian national consumption--enough to stretch out existing stocks for only two months. And there is growing evidence that the economy is running down. At present, Rhodesia is earning foreign exchange at an annual rate of 70 million pounds, as compared with 1964 earnings of 143 million.

But if Smith brings the bluff off past June, the British should seek a mandate from the UN to escalate the sanctions. One possible means would be to extend the sanctions to include areas now aiding the Smith regime--South Africa, Portuguese Mozamzique, and Angola. The British might also attempt to seal off the borders by military intervention.