The Civil Aeronautics Board yesterday awarded Pan American World Airways the right to restore the China Clipper to commerical service after an absence of more than 30 years from one of civil aviation's storied routes.

President Carter technically has the right to change the board's ruling, but assuming that does not happen Pan Am is planning to begin three round trips a week starting Dec. 1 between Nw York or San Francisco and Peking. tSome of the flights will stop in Shanghai.

The new service was included in a trade package signed by Carter and Chinese officials last month at the White House. The pact specified that two U.S. carriers may fly the U.S.-China route, but the government will not pick the second carrier until 1982. China's national airline, CAAC, is expected to begin flying to the United States about the same time.

Pan Am Chairman William T. Seawell said, "All of us at Pan Am are delighted that the China Clipper will fly again. We are most pleased with the decision of the CAB and will seek to commence air service to China as soon as we receive formal permission."

Pan Am was one of five U.S. airlines seeking the route, which has not been served since 1949 when virtually all commerce ceased between the United States and the People's Republic of China. Pan Am and Northwest Orient were the last U.S. carriers and were regarded as the most likely winners, partly because they both have routes to Tokyo, an important intermediate stop. p

Also in the competition were United Airlines, Trans World Arlines and Transamerican Airlines. "It was clear from the beginning that if Pan Am didn't have it locked up, they had a leg up to it," an official of one of the disappointed losers said yesterday.

CAB Chairman Marvin S. Cohen said the choice between Pan Am and Northwest was very close. "There was obviously three votes out of five for Pan Am," Cohen said. "So we decided those three might as well go ahead and start writing the recommendation to the president. Favoring Pan Am were board members George A. Dalley, Gloria Schaffer and James R. Smith. Cohen and members Elizabeth E. Bailey seemed to be leaning toward Northwest.

Cohen said he does not know whether the former recommendation will include a minority opinion. "I kind of doubt it," he said. "It's so close, I couldn't make a convincing argument for Northwest over Pan Am."

Schaffer said she thought Pan Am "offered the best service proposal" with good connections from both coasts. "One of Pan Am's two San Francisco flights will be changed in April to Los Angeles. Northwest could offer only Seattle on the West Coast.

Schaffer also used the word romantic in agreeing that Pan Am had a historical advantage in the competition. Pan Am pioneered passenger service across the Pacific in the 1930s with airplanes it called China Clippers.

Spokesman Merle Richman said that Pan Am projects a first-year market of 28,900 passengers between the United States and China, and expects another 28,000 will board in Tokyo. Fares are subject to approval by China, but Pan Am is proposing an economy-class fare of $651 between the West Coast and Peking and $881 between New York and Peking. Various discount fares will be proposed.

In another important action yesterday, the CAB said it will recommend that Carter designate Pittsburg and Baltimore for nonstop service to London. The two cities were among four competing for designations as new "gateways" from the United States to Great Britain.

The CAB recommended TWA as the airline to provide the Pittsburgh-London service and World as the airline to provide the Baltimore-London service. American Eagle is the backup carrier for each route.

The airline deregulation act permits the president to overturn CAB recommendations only for foreign policy or national defense reasons, not on economic grounds. That act came into force after Carter overturned a 1977 CAB recommendation that Pan Am be awarded the Dallas-Loundon route. Carter gave it to Braniff International, and there were complaints that politics had played too prominent a role in that decision.