John J. O'Connor III, husband of Supreme Court Justice Sandra Day O'Connor and a senior partner in one of Arizona's most prestigious law firms, will become a partner in the Washington firm of Miller & Chevalier on Jan. 1.

O'Connor, who reportedly began looking for a position with a local firm shortly after his wife's confirmation last September as the first woman on the court, yesterday declined to comment on his new job, saying only that he was "very pleased" that he will be joining Miller & Chevalier, a highly regarded local firm, especially in federal tax matters.

John S. Nolan, a member of the firm, said O'Connor was "recommended to us by lawyers in Phoenix who are friends of ours." He said the firm approached O'Connor about one month ago to discuss the possibility of his joining.

"We were pleased that we were compatible with his interests and he with ours," Nolan said. "He is an expert in litigation and has a lot of appellate experience and we have a lot of appellate work," Nolan added.

Another important area of compatability was the scant chance that O'Connor's work will conflict with his wife's duties as a justice. Justices and judges are supposed to disqualify themselves from any case in which a spouse has an interest,either as a party to a case or as a lawyer in a case.

"We discussed the extent that we have cases before the Supreme court," Nolan said, adding that the 65-year-old firm, which has 55 lawyers, "very seldom" represents clients in the Supreme Court, estimating that they had done so only three or four times in the last 30 years.

In her brief tenure on the court, Justice O'Connor already has disqualified herself from an unusually large number of cases. This week alone, she disqualified herself in four cases in which the court was deciding whether to review lower court decisions, and she has disqualified herself from at least three other cases argued before the full court.

Like the other justices, however, O'Connor has declined to explain why or how many of her disqualifications are related to her own interests and how many to those of her husband and his Phoenix law firm, Fennemore, Craig, von Ammon & Udall, which specializes in corporate matters in general and mining interests in particular.

John O'Connor, who has been a member of that firm since 1957, has been commuting to Phoenix since his wife's confirmation.