The Nuclear Regulatory Commission yesterday ordered construction halted on the troubled Zimmer atomic power plant 30 miles east of Cincinnati and suggested it may be difficult for the facility -- which is 98 percent complete -- to ever obtain an operating license because of construction defects.

James G. Keppler, the NRC regional administrator who a year ago imposed a record $200,000 fine on Zimmer's builder, Cincinnati Gas and Electric Co., said yesterday "there have been more quality assurance problems discovered" in construction of the $1.7 billion facility than at any other U.S. nuclear power plant. "Whether that translates into an unacceptable plant remains to be seen," Keppler said. "But problems are being found at a rate faster than they can be redressed. It is going to be very hard for us and the utility to find this plant meets all the commission's requirements."

Cincinnati Gas and Electric, in appealing to the NRC to allow work on the plant to continue, said it was bringing in the Bechtel Corp. as joint manager of the project and proposed that Bechtel be allowed to immediately undertake a three-week assessment of the problems. But the NRC, while agreeing that an independent audit of the plant's quality assurance program was necessary, said it wanted to "look into" the question of whether the review should be performed by Bechtel "in view of some problems at other nuclear plants involving Bechtel."

"Bechtel has done some jobs well, but they've done some not as well as I would like," Keppler said. He said that at the Midland atomic power plant under construction in Midland, Mich., where Bechtel is both the contractor and the architect-engineer, "they've had a number of quality assurance problems -- some of them quite serious.

"I want to understand how these problems are being handled," Keppler said. He said it would take him about a week to decide whether Bechtel should be allowed to conduct the review at Zimmer.

The commission, in ordering an immediate halt to work at Zimmer and giving Cincinnati Gas and Electric 25 days to contest its ruling, split 3 to 2 with commissioners Thomas M. Roberts and John F. Ahearne in the minority. Ahearne said he agreed with the substance of the order but would not have put it into effect immediately.

Roberts, a Reagan appointee, said he felt the commission's action was "precipitous" and thought that the three pages of "major construction deficiencies" cited by the staff in the order halting the project do not "show that the public health and safety requires immediate suspension of all" work at Zimmer.

The NRC halt-work order came a day after it was disclosed that a federal grand jury is investigating alleged falsification of quality assurance records and harassment of quality control inspectors at Zimmer.

Thomas Devine, attorney for the anti-nuclear Government Accountability Project, which has filed a number of allegations with the NRC critical of construction work at Zimmer, said he had been subpoenaed to appear before a grand jury in Cincinnati. Devine said he had been ordered to bring notes and other records on his group's investigation of Zimmer.