Unexplained delays by the White House and Justice Department in asking Congress to grant it subpoena powers today forced the presidential commission investigating the accident at Three Mile Island to call off its first two days of hearings at the scene of the accident.

An embarrassed John Kemeny, chairman of the presidential commision, postponed indefinitely the testimony the commission had planned to hear from five Pennsylvania state officials and the four operators who were on duty March 28 when the accident occured. Kemeny blamed the postponement on the fact that he had not received authority from Congress to hear witnesses under oath.

"I want to apologize to the governor of Pennsylvania (Richard Thornburgh) and all other witnesses for this inconvenience," Kemeny said at the Penn State University gymnasium where the hearings were to have been held. "The fundamental issue is the commission's need to hear testimony under oath. This puts us in a painful dilemma which is not easy to resolve."

The commission had considered taking unsworn testimony because of all the preparations it had made for the hearings and because of its tight deadline (Oct. 25) to report its findings to President Carter. Following a 15-minute debate, however, a majority of the commissioners decided testimony under oath was more important.

"We've been lied to and the only way to get the truth is under oath," said Anne Trunk, a Middletown resident who is a member of the commission.

Kemeny was under the impression that the White House and Justice Department had asked Congress at least two weeks ago for power to subpoena witnesses and have them testify under oath, in part because on April 26 the two had reached agreement on legislation granting those powers. But the legislation apparently did not reach the Senate Judiciary Committee until last Friday.

On Tuesday of this week, Judiciary Committee staffers told White House and Justice staffers that Sen. Edward M. Kennedy (D-Mass.), Judiciary chairman, did not like the wording of the legislation that would permit the commission to hold closed-door meetings. The commission had asked for the right to go into closed sessions to discuss which witnesses and what documents to subpoena.

"When we decide who to subpoena and what to subpoena, we want to do it in executive session without tipping our hands," Kemeny said at a press conference called hastily this morning after the hearing were postponed. "Otherwise it's like holding a grand jury in public."

A spokesman for Kennedy said the commission already has the power to discuss subpoenas in closed sessions. All a presidential commission has to do to meet in closed session, the spokesman said, is request permission each time it does so from President Carter or the administrator of the General Services Administration acting for the president."We felt that authority was sufficient," The spokesman said. "We felt that any additional authority would be controversial and delay passage of the bill, so we suggested they remove it. As of this moment, we've heard nothing from the White House or Justice on what they want to do."

A White House aide who asked not to be identified admitted there had been some debate about the type of legislation and its wording before it was sent to the Judiciary Committee. Said the aide: "It's lawyers arguing. They got bogged down in it."

Whatever the reasons, the 12-member commission till lacked authority to hear witnesses under oath. Since its members had come to Middletown at federal expense to hear the witnesses, the affair began to look like a comedy of errors with the commission caught in the middle.

Once the problem was perceived in Washington, there was swift movement to correct it. In his capacity as judiciary chairman, Kennedy took the floor of the Senate at 2:51 p.m. today and asked that the Senate grant the commission power to subpoena witnesses and hear their testimony under oath. He left open the question of whether the commission could hold its own closed-door sessions.

At 2:52 p.m., Kennedy's motion passed by a vote of 2 to 0. The only other senator present was John Warner (R-Va.) who joined Kennedy in passing the resolution. On Monday the motion goes to the floor of the House, which needs only to give its voice consent to make it law.

Even though it seemed likely the House might approve the move on Monday, it was too late to correct the mistakes that led to the postponement of two days of hearings and the dismissal of no fewer than nine witnesses, including Pennsylvania Gov. Thornburgh.

The commission decided today to go ahead with its plan to tour the Three Mile Island site, including the containment building of the sister nuclear reactor to the plant that was striken by the accident and shut down on March 28. On Saturday the commission will hear area residents who evacuated their homes when Thornburgh suggested during the week of the accident that they might wish to do so.

Commission Chairman Kemeny and most of the other 11 commissioners decided they did not need to take testimony under oath from the residents, since these witnesses had no liability for the accident and would have no reason to cover up any details regarding it. CAPTION: Picture, Anne Trunk: "We've been lied to and the only way to get the truth is under oath." UPI