Judge Abner J. Mikva says neither his congressional activities nor his wife's brief employment at the National Highway Transportation Safety Administration conflicted with his ruling on a key auto-safety issue handed down earlier this week.

The decision, on behalf of a three-member U.S. Court of Appeals panel, overturned the administration's position on air bags and automatic seat belts and represented the sharpest setback thus far for the Reagan administration's deregulation campaign.

Following his customary procedure, Mikva said yesterday that he carefully weighed his participation in congressional debates on auto-safety rules before concluding there was no conflict of interest in taking the case. Another factor he had to consider was that his wife had worked briefly for NHTSA in the last days of the Carter administration. The judge concluded that, too, did not present a conflict of interest.

Mikva said he was sure the airbag issue came up at some point during his eight years in Congress, where he represented a Chicago-area district. However, he said, he never played an active role on the issue by speaking on the floor or in the committee about auto safety.

"As a rule, when I played an active role in Congress, I excuse myself from any case," involving those issues, Mikva said. However, where he was just a voting member, he does not excuse himself from the case. "Otherwise, I'd not hear any cases."

Additionally, Mikva later recalled, he left Congress before the House took its most important vote supporting airbags in late 1979.

Mikva also said he "checked very carefully" his wife's role at NHTSA before taking the case. Zoe Mikva, a former elementary schoolteacher, worked at the agency from September through December 1980 as a political appointee in the Office of Traffic Safety Programs.

Her main job, she said yesterday, was to review state safety programs and encourage the states to come up with innovative consumer education programs about drunk driving, the benefits of using helmets on motorcycles, the 55-mile-per-hour speed limit and other safety issues.

"I had absolutely nothing to do with passive restraints," she said yesterday.

Mikva said that after he was assured his wife played no role in the airbag controversy, he decided to take the case--but "never discussed it with her after that."

In his ruling for the court, Mikva overturned the NHTSA's decision to repeal a 5-year-old rule that would have required auto companies to install passive passenger restraints in all new cars by September 1983, saying the decision was "arbitrary and unlawful" and based on unfounded evidence.

Yesterday, NHTSA officials still had little to say on the court ruling.