President Carter is expected to nominate a 34-year-old lawyer named Peter Bradford, a onetime chairman of Maine's Public Utilities Commission, to chair the Nuclear Regulatory Commission.

A six-year member of Maine's PUC, Badfaord also served in 1968 as a member of Ralph Nader's Public Citizen organization.

Bradford's brief stint with Nader was spent studying the Federal Trade Commission and came long before Nader began examining the nuclear power industry.

The White House decision to nominate Bradford to become the fifth of five commissioners on the commission ends speculation that Federal Energy Administrator John F. O'Leary would move to the NRC and became chairman.

"0'leary's not going over there," a White House source said yesterday. "He's staying with [James R.] Schlesinger to go with the new Department of Energy when it is formed."

Bradford's nomination to the NRC will go to the Senate sometime next week, it is understood.

Already awaiting confirmation by the Senate for a one-year term is Kent Hanson, a nuclear engineering professor at Massachusetts Institute of Technology, and for a four-year term is Joseph Hendrie, a physicist at Brookhaven National Laboratory on Long Island. These nominations were made last week by Carter.

At present, the NRC is functioning with only two commissioners. One is Victor Gilinsky, who has two years of a five-year term left. The other is Richard T. Kennedy with three years remaining to serve.

A 1964 graduate of Yale University Bradford taught in Greece for one year before returning to Yale Law School where he earned his law degree in 1966. After his work with Nader, Bradford worked in the office of former Maine Gov. Kenneth Curtis who is now chairman of the Democratic National Committee.

Curtis appointed Bradford to Maine's PUC in 1971 and made him executive director of the governor's task force on energy. Three years later, Bradford was made PUC chairman, a position he held untiil he was removed by the governor, James Longley.