Henry Tenenbaum, for two years the host of WDVM's nightly "PM Magazine" show, has been hired as a reporter by NBC News, sources there confirmed yesterday, and will be a contributor to a planned new weekend edition of "The Today Show" set to premiere next January.

Tenenbaum, a general assignment reporter who covered offbeat or whimsical happenings for WDVM News prior to the "Magazine" assignment, will begin work at the NBC News bureau here in September, according to Sid Davis, bureau chief. "We've known about him for years for his work here in Washington," Davis said.

Tenenbaum was co-host, with Susan Goldwater, of "Magazine" when the program was launched in March 1979, but became sole anchor after Goldwater and a succession of other co-hostesses left the show. In May, the station announced that it and Tenenbaum had "mutually agreed" he would not continue on the program beyond the June 30 expiration date of his contract.

Plans for the weekend version of the "Today Show" are not yet firm, Davis said, but Tenenbaum is slated to contribute regular features to the program, and may be appearing on the weekday "Today Show," granddaddy of all network morning information programs, until the new edition is ready for air.

"I'm real excited about this," said Tenenbaum, 34, yesterday. "I couldn't ask for a better opportunity." Asked if his parting with WDVM had been amicable, Tenenbaum said, "No, not terribly." He said the station had caved in to pressure from Westinghouse Broadcasting, which franchises the "PM Magazine" format here and in other cities, to make the program more of a "Ken and Barbie type show," and he wanted the emphasis on "honest and genuine people."

Tenenbaum leaves today on a 55-day world tour, after which he will report to his new desk at NBC. "I'm almost overwhelmed with an abundance of joys," he said.

Although the Tenenbaum announcement has not yet officially been made by NBC, Davis said the network has made official its agreement with the Chinese government to set up the first news bureau operated by an American TV network there. The bureau, in Peking, will open "later this summer" at a date yet to be agreed upon.

Davis said the new bureau will be staffed with only one correspondent, but that crews can be brought in as stories warrant. Although he declined to name correspondents under consideration for the bureau, or to characterize it as either a plum or booby-prize position, Davis did hail it as "a historic, precedent-making assignment."

NBC News president William J. Small visited China in March and yesterday received word from Chinese officials that the deal was on.