Donald McHenry, THE U.S. ambassador to the United Nations, has warned the Carter administration that Britain is "on a very wrong course" in lifting economic sanctions against Rhodesia. He said such punitive measures could not be rescinded without "proper" U.N. Security Council action.

McHenry's argument, contained in a government memorandum, conflicts with a Britain plan, which urges an immediate end to U.S. sanctions against Rhodesia.

Britain is scheduled to lift its sanctions today as a British governor arrives in Salisbury to take charge of the breakaway colony. It argues that the move restores Rhodesia to legality and thus ends the need for punitive measures imposed after Rhodesia's white minority government unilaterally proclaimed independence.

British sources here said U.S. failure to make a similar move would open the way for the Patriotic Front guerrilla leaders to string out the current peace talks in London and in effect delay an early settlement.

According to the memorandum written by William Harrop, deputy assistant secretary of state for African affairs, McHenry has urged the administration to persuade Britain to seek Security Council approval for termination of punitive actions against Rhodesia.

"We should argue forcefully with the British to save them -- and us -- from themselves," the memorandum quoted McHenry as saying. "The time to act is now while the Patriotic Front and the front-line African states are on board." The five front-line states, which support the guerrillas, are Angola, Zambia, Mozambique, Tanzania and Botswana. ( [TEXT OMITTED FROM SOURCE]

Apart from arguing against British policy, McHenry's argument reveals a split in administration ranks over sanctions.

In a statement last month, President Carter said he would be "prepared to lift sanction when a British governor assumes authority in Salisbury and a process leading to impartial elections has begun."

In a meeting with 10 black leaders that same day, Carter said he would sustain punitive measures until a new black majority government is elected in Rhodesia, according to Randall Robinson, one of the leaders present.

The memorandum said McHenry felt "strongly" against unilateral lifting of sanctions.

A bill approved by the Senate last week directs the president to lift U.S. sanctions upon the arrival in Salisbury of a British governor, or by Jan. 31, unless Carter considers the move as harmful to U.S. national interests.

U.S. sources said yesterday that the administration did not want to be "on the collision course" with Britain. At the same time, they said, the United States would favor some form of U.N. action before U.S. sanctions are lifted.

Britain argues that U.N. action is not needed sinch Rhodesia's return to colonial status restores London's authority, at least temporarily. U.S. officials, however, pointed out that the original sanctions against the breakaway colony were imposed by the United Nations, at Britain's request.

Officials here were hoping that the London talks between Patriotic Front leader and the Zimbabwe-Rhodesia government of Abel Muzorewa would reach a peace settlement soon. In that case, the administration would not have to make a difficult choice.

U.S. sources emphasized that the suden departure of a British governor for Salisbury yesterday comes before the London talks had reached a cease-fire agreement. This is a new and unanticipated wrinkle.

These sources pointed out that when Carter asserted that he was prepared to lift sanctions following the arrival of British governor in Salisbury, "the assumption was that the governor would take over following a final agreement in London."