SEN. KENNEDY, who has just spoken out on China, represent those China hands inside and outside the administrations who believe that the United States should move quickly to take the principal uncertainty out of its relationship with the People's Republic. It could do this by ending formal ties with Taiwan and opening a full embassy in Peking. These experts fear that, if Washington does not move, Peking may seek an accommodation with Moscow - to the United States' geopolitical disadvantage. They assert, sometimes with passion, that the right and natural thing for the United States is to maintain close ties with China and that, after a 30 year hiatus, the time to do it has come.

We share the Kennedy group's concern to set the United States' China policy on an even keel. Geopolitical comforts could reasonably be expected. It is unnatural for the United States still to be interfering, by mainkining formal ties with Taiwan, in the Chinese civil war. We agree that the current military and political equations are such that Taiwan does not have to fear an invasion from the mainland.

But the more we think about it, the queasier we get. Sen. Kennedy's group holds that the administration can have its cake and eat it, too: easy normal relations with Peking and ensure the security of Taipei.How? By "careful diplomacy" - careful formulations, the conveying of assurances and the like. Mr. Kenedy, however, would not wish to ask Peking to renounce the use of force to regain Taiwan - that would challenge its insistence that the Taiwan question is an internal Chinese matter. He seems insensitive to the psychological sense of isolation that would surely be given in Peking to a recalculation of the political and military odds. The senator betrays a certain unease - a becoming unease, we would say - in indicating that Peking would be expected to sit still while the United States continued to sell Taiwan arms. But would Peking sit still?

It would be more straightforward, we think, to argue that the need is so great to consolidate relations with Peking that 1) it is worth weakening the United States' strong assurance in the Shanghai comunique of 1972 that it would not step back back from Taiwan until the Taiwan question had been settled peacefully by the Chinese, and 2) it is even worth casting a certain cloud over the validity of this and other American commitments. But that is a hard case to make on the merits and, of course, it is an impossible case to sell politically. We presume Secretary of State Vance will have more modest purposes in mind as he arrives in Peking Monday.