The first winners of the Praemium Imperiale, a new international prize for lifetime contribution to the arts and intended to compare to the Nobel Prize in purpose and scope, will be announced at a Sept. 15 luncheon in New York. The Japan Art Assn., sponsor of the prize, said Monday that prizes of $100,000 each will be awarded in five fields: architecture, music, theater and film, painting and sculpture, areas not represented by the Nobel Prize. The announcement luncheon will be hosted by David Rockefeller, the North American representative of a blue-ribbon International Committee of Advisers that nominated candidates for the Praemium Imperiale to the Japan Art Assn. The other advisers are Jacques Chirac, former prime minister of France; Amintore Fanfani, former prime minister of Italy; Edward Heath, former prime minister of Great Britain, and Helmut Schmidt, former chancellor of the Federal Republic of Germany. The 1989 winners will get their awards at an Oct. 27 ceremony in Tokyo.