The most coveted British diplomatic post abroad, ambassador to the United States, went today, somewhat unexpectedly, to Sir Oliver Wright, a retired career envoy who seems never to have stepped wrong in a long succession of challenging jobs.

Wright, 61, has amassed effusive clippings in a lifetime of service that ended as ambassador to West Germany. "The most popular ambassador Britain has had in Bonn," the London Times said when he retired last year. The Times praised his "disarming bluntness," his "humor" and added he is "an unpompous figure in brightly colored shirts, sometimes frayed at the cuffs and with a gift for putting difficult problems in simple terms."

The description of Wright is not unlike those offered by friends of Britain's outgoing ambassador in Washington, Sir Nicholas Henderson, who became a familiar figure to American television viewers as a salesman for Britain's policies in the Falkland Islands dispute.

Wright chose the Washington job over another prestigious post that he was scheduled to take this summer, Master of Christ's Church College at Cambridge University, his alma mater.

"It was a conflict of duties with affections," Wright said in an interview today. "I felt a sense of obligation to the college, which went to the trouble to elect me, and a sense of obligation to the crown, which I served for 40 years. The crown won."

The decision may have been eased by the fact that his selection for the Cambridge position was reportedly opposed by some academics who felt it should be filled by a distinguished scholar. The post had been filled by the famed historian J.H. Plumb. Wright was elected after what one account called "a long and bitter contest that closely resembled the plot of C.P. Snow's novel 'The Masters,' which was based on an election at Christ's."

Henderson, who arrived in Washington nearly three years ago, shortly after the election of Prime Minister Margaret Thatcher's Conservative government, had been scheduled to retire. For weeks, the diplomatic communities in Washington and London have been speculating about his successor.

A number of well known British figures were mentioned, including Lord Carrington, who resigned as foreign minister in penitence for failing to prepare the government adequately in advance of Argentina's invasion of the Falklands, and Sir Christopher Soames, a former ambassador to France who is married to the daughter of Winston Churchill.

Instead, Thatcher and her new foreign secretary, Sir Francis Pym, chose Wright. In doing so they repeated the earlier example of recalling Henderson, who was also an ambassador in Bonn and had retired as Britain's ambassador to France. Unlike the United States, most British ambassadors are drawn from career diplomatic ranks. Once retired, however, the envoys fall into the category of political appointees.

Nonetheless, Wright insisted today that he had not been chosen out of any known proclivity for Thatcher's conservative philosophy. "I have no politics, except very privately," he said. "I advise the government on what policy should be and then I carry out policy the government determines."

Wright will come to Washington with his wife, Lillian. Their youngest son is married to an American and lives in Los Angeles, where he is in real estate. One incentive of his new job, Wright said, is to get 3,000 miles closer to his grandchildren.

But the job has other attractions. "Washington is a unique job," he said. "It is our embassy to a friendly superpower--the only one friendly superpower." As a diplomat, he added, it enables him to use "all the tools of the trade." Wright said he looks forward to the public aspects of the position, the speechmaking, the television appearances: "One of the attractions of Washington is that it is such an open society."

Although he served years ago as a vice-consul in New York, Wright has never before been permanently assigned to Washington. Among his other jobs were ambassador to Denmark and government representative in embattled Northern Ireland. He was an aide to two prime ministers--one Conservative and one Labor--and held top administrative posts in the Foreign Office.

He had often been mentioned as a possible ambassador in Washington, but never made it before reaching the mandatory Foreign Office retirement age of 60. Now the post is finally his. "It's a marvelous job," Wright exclaimed today.