The Carter administration intends to formalize today its past offers to sell military-related equipment to China.

The formal step, sources said, will be the announcement that the administration has approved export to China of assorted computer equipment, radars and trucks and has given permission for some U.S. companies to brief the Chinese on their products.

Although Pentagon officials insist no weapons will be sold to China, they concede a new military relationship is indeed developing.

Defense Secretary Harold Brown said as much in toasting his Chinese counterpart, Vice Premier Geng Biao, at a dinner Tuesday night.

"The United States looks forward to the continued step-by-step strengthening of ties between our two defense establishments as an integral part of our effort to normalize all facets of our relationship. We do not expect this to happen in a rapid or dramatic way" but the process "has already begun . . .

"We have developed the procedures necessary to implement the policies on dual use technology transfers and the sale of support equipment," Brown continued.

Geng Biao, in returning Brown's toast, voiced a tough line against Soviet and Vietnamese aggression, declaring that "since they represent a strategic challenge, they call for a strategic response."

He said the Chinese "are making a historic long march" to modernize, including their defenses. "The Chinese people are determined to fight unremittingly against Soviet hegemonist aggression and expansion," he said.

Geng Biao took at least one great leap forward during his stay here. At President Carter's invitation he watched the movie, "The Empire Strikes Back," son of "Star Wars," at the White House Monday night.