IT HAS to be said of Sen. Jesse Helms's abuse of senatorial prerogatives that his ends are not trivial. He seeks to wrest control of an important part of the foreign policy of the United States from the president and from the people Mr. Reagan has appointed to high office.

But the means he employs are petty. In the latest instance he has prevented the Senate from voting on the nomination of the well-qualified Winston Lord to be the American ambassador to the People's Republic of China. The nomination was approved by the Foreign Relations Committee by a 16-to-1 vote five weeks ago. Majority Leader Robert Dole would like a vote on it. So would Foreign Relations Chairman Richard Lugar. Mr. Helms's ultimate chances of achieving his stated goals are not great. But his taking hostage of Mr. Lord is no small embarrassment to the United States, to the Reagan administration and especially to the Senate.

Sen. Helms's stated complaint is that Mr. Lord and the Agency for International Development bureaucracy are not sufficiently faithful to the Kemp amendment, a measure aimed against American participation in foreign family-planning programs that condone coercive abortions. Such abortions evidently have taken place in China, but Chinese officials assert, and knowledgeable foreigners agree, that the U.N.-supported family-planning program has, if anything, acted as a restraint on such practices.

But this is not enough for Sen. Helms. He wants to deny the administration the slight room the law provides to stay involved in the worldwide work of the United Nations Fund for Population Activities so long as the fund does not support congressionally proscribed programs in China. He would keep American money from going by any channel for family-planning measures that, by preventing unwanted pregnancies, prevent abortions. The plain effect of the Helms policy is to foster abortions.

The senator suggests that Mr. Lord and the AID hierarchy do not understand the president's desires in this matter. Nothing in the record indicates that this is so. What Sen. Helms is really suggesting is that the president is a figurehead manipulated by aides. This is patronizing nonsense.

Mr. Helms has held up appointments before, and he has been routed without achieving all his stated aims once the Senate roused itself to stare him down. The Senate must rouse itself once more. And Mr. Reagan should make it clear that administration policy is not determined by the senator from North Carolina.