"I'm not an actress. I'm a former actress," insisted Nancy Mehta, "that is, unless you consider being what I am to be acting." The willowy, fine-boned woman was talking about being the wife of the dashing, sometimes headstrong new music director of the New York Philharmonic, Zubin Mehta.

He demonstrated his command of the formidable New York ensemble at two Kennedy Center concerts over the weekend. And later, his wife conducted herself equally well as she held court, dressed in glistening gold lame, at an Indian Embassy supper following the Saturday night concert.

If there was a touch of Hollywood in the Mehta's demeanor, it was no accident. For the first nine years of their marriage, they lived in the laid-back luxury of Brentwood while Mehta was conductor of the Los Angeles Philharmonic.

"We would never have met if my acting had not brought me to the coast in the late '60's to do some work for Columbia," she recalled. On stage and film she is known as Nancy Kovack.

"And we have deliberately not given up our house. It's wonderful to go back after months of bad weather in New York. Hardly anyone knows it, but Zubin and I slipped back out there for several days just a few weeks ago.

The surprise announcement in 1976 that Mehta would take over the New York orchestra he had once denounced (later to his regret) for "stepping over conductors," came as good news to his wife."After all, New York is as much home as any place has been for me. I spent 13 years of my acting career there. But this first year back has meant a year of hotel living. Finally, we bought a house-on the East Side-but we won't get possession until July," she said.

Earlier on Saturday, Nancy Mehta had brought a dark suit to the embassy so that her husband could change into it from his tails after the concert. "I wear tails even if no one else does," explained Mehta. "My predecessor (Pierre Boulez) changed the orchestra's dress to tux. But I find them awkward to conduct in. You need more room; there has to be some air flow." At the embassy, Ambassador N.A. Palkhivala and his wife honored Mehta as India's most celebrated citizen in this country. The ambassador noted that both he and Mehta are Parsis, a small sect that fled Persia for Bombay in the 8th Century. CAPTION: Picture, Nancy and Zubin Mehta, by Gerald Martineau-The Washington Post