WHITE HOUSE national security adviser Richard V. Allen had an interesting comment Sunday on Peking's unprecedented campaign to bring about a peaceful unification of the mainland with offshore Taiwan. He said that the administration was watching "with great interest, and perhaps some anticipation, the development of any dialogue" but that Taiwan's response was "entirely a matter for the Taiwanese to decide."

Given President Reagan's longstanding commitment to Taiwan and his determination not to be seen hustling American friends anywhere into concessions to Communist powers, this was an expectable answer--and a reasonable one. The intriguing thing, however, was that it was an independent American answer and not an echo of Taiwan's. For Taiwanhas denounced the Peking campaign and reiterated its condition for unification--the People's Republic must renounce communism. The Reagan administration, which after a fitful start seems to be resuming its predecessors' effort to "normalize" relations with Peking, makes no such demand. On the contrary, it watches "with some anticipation" for dialogue across the Formosan Strait.

Is Peking's peace initiative an attempt to "cut our throats and cut off our hands," as Taiwan defensively suggests? It is notable, if not definitive, that over a period of time the People's Republic has set aside the rhetoric of "liberation" in favor of a line suggesting gradual peaceful accommodation. Just in the last few weeks Peking has added some sweeteners to its longstanding offer to let a returning Taiwan retain its economic system and armed forces in a "special administrative region": direct party-to- party talks, "posts of leadership" in Peking, a burial site at the ancestral home for Chiang Kai-shek, the late father of the current Taiwanese president and the legendary foe of the Communist regime. Last Saturday, Peking for the first time observed Taiwan's national day, which marks the Nationalists' overthrow of China's last dynasty in 1911.

The Nationalists set up their government on Taiwan in 1949 after being defeated by the Communists, and they have never stopped pressing their claim to be the legitimate ruler of the mainland, too. It has seemed a forlorn claim, but it has kept alive the common Chinese belief in a single China--the belief on which the mainland plays now. It may be too early to say what will come of the current Chinese unification effort, but it is hard to look at the history and the longing and to conclude that China will never again be one.