It is no longer within the power of America to try to be first in world science in many fields, George Keyworth said yesterday in his first address as the president's White House science adviser.

Instead, he recommended concentrating the nation's energy on a few of the most productive fields.

". . . Our country has relinquished its preeminence in some scientific fields, while others are strongly threatened through efforts in Europe, Japan or the Soviet Union," Keyworth said in remakrs prepared for delivery last night before the American Association for the Advancement of Science here.

"It is no longer within our economic capability, nor perhaps even desirable, to aspire to primacy across the spectrum of scientific disciplines. The constraints of reality require discrimination and vision. . . . We must strive to identify those disciplinary areas where vitality is required to support industrial military [technologies] . . . as well as those with particular scientific promise . . . measured in terms of probability of major breakthroughs."

In a press conference at the meeting, Keyworth said that two obvious areas are applied computer science and basic genetic research.

He said one of the most important science priorities is to reallocate federal dollars to basic research likely to produce breakthroughs and applied research that will be pertinent to the country's economic well-being.

Keyworth also warned the assembled scientists that he will not serve as the scientists' representative at the White House. ". . . Nowhere is it indicated that the Office of Science and Technology Policy or its director [the science adviser himself] is to represent the interests of the science community as a constituency. . . ."