The Nuclear Regulatory Commission yesterday half-heartedly authorized the restarting of the Salem atomic power plant, site of the most serious mishap since Three Mile Island, after concluding that little more can be done in the short run to improve operation of the facility.

Chairman Nunzio Palladino confessed to a "nagging concern" about whether the management of the New Jersey plant has "really reoriented" its thinking on the need for improved operating and maintenance procedures since the failure of the reactor's emergency shutdown system on Feb. 22 and 25.

But Palladino nevertheless led the panel in voting 4-to-0 to permit Public Service Electric & Gas to put the reactor back into operation. Only Commissioner Victor Gilinsky, who left before the vote, favored keeping the plant closed.

The NRC staff reviewed for the commission the steps the utility has taken to improve training, quality control and maintenance at the plant, which has had three additional mishaps since being closed two months ago.

And last week, the NRC staff said, workers installed electrical devices at Salem to replace those involved in the February incidents without noticing that the new devices were broken.

"There's still something a little worrisome in the management's attention to the maintenance area," said Harold R. Denton, director of nuclear reactor regulation.

But William J. Dircks, NRC executive director for operations, said that management's actions since the incident "seem to be moving in the right direction . . . . I don't think there is too much more we can do."