The Nuclear Regulatory Commission staff yesterday resumed proceedings on pending applications for new nuclear power plant licenses, ending a three-month freeze it imposed after the Three Mile Island accident in Pennsylvania.

Harold R. Denton, director of the NRC's reactor regulation office, said the first completed application for an operating license probably will be ready for a final decision in about a month. The plant, probably Salem, II in New Jersey or North Anna II in Mineral, Va., could then load its uranium fuel immediately and start operations about a week later.

In a letter to the commission announcing the action, Denton said all applicants for construction permits and operating licenses will have to agree to make certain changes in design and procedure before the applications can be approved.

Denton said there are 24 such changes, agreed upon by a task force that drew the lessons learned from Three Mile Island, the NRC's special advisory commission on reactor safeguards and Denton. The changes will all have to be implemented by Jan. 1, 1981, in the nation's 70 operating reactors, as well as in any new ones.

"It is unlikely that any of the other review groups will come up with anything that would foreclose these changes," Denton said in an interview. interview. "By and large this covers the hardware issue . . . The other groups will be making more policy recommendations than hardware ones."

He referred to the Presidential Commission on Three Mile Island, which is holding hearings, the NRC'S special investigatory commission and several congressional inquiries expected to extend well into the fall.

Denton announced the three-month freeze May 21, calling it "suspended animation" for pending licenses. It affected four applications for operating licenses and five construction permit applications in six states.

During the last three months, the NRC staff dissected the events of the March 28 accident at the Middletown, Pa., plant and decided what other plants needed to do to avoid a similar occurence. Some of the 24 changes have been made, some will have to be made before the new plants may start up or by Jan. 1, 1980, and the rest must be finished a year later.

"It is my judgment that the Three Mile Island II-related actions being taken . . . are necessary and sufficient for the continued safe operation of operating plants and for the resumption of staff licensing activities," Denton said in his letter to the commission.

The changes include installation of new equipment, including emergency power supplies, indicators of valve positions, high-range radiation monitors and valves to release any future hydrogen bubble. They require reanalysis of plant shielding, retraining of operators and the positioning of a trained technical adviser on each shift.

Other changes involve testing of valves like those that stuck during Three Mile Island, rewriting the procedures in several areas and revamping other shift and reporting practices.

Denton's action was denounced immediately by the Union of Concerned Scientists, a Massachusetts-based group critical of nuclear power, as "a return to business as usual."

Peter Franchot of the UCS said the other review groups looking into Three Mile Island also planned to consider technical questions and that their results may differ from the NRC'S. At a minimum the NRC should wait until the presidential commission reports." he said.

The applications affected by the three-month freeze were construction permits for the Perkins 1, 2 and 3 plants in North Carolina and for Black Fox 1 and 2, in Oklahoma; and operating license request for Salem 2, North Anna 2, Diablo Canyon in California, Sequoyah in Tennessee and McGuire in North Carolina.