In an extraordinary Senate confirmation hearing, President Reagan's nominee to a federal energy board spent almost two hours yesterday explaining a past that includes two drunken driving arrests, an inebriated fight with a subordinate in a Capitol Hill drinking spot and accusations by colleagues that he abused his power as former chief counsel of the Senate Energy Committee.

Members of the committee indicated that they expect to confirm Charles A. Trabandt, 43, their former employe, for a vacancy on the Federal Energy Regulatory Commission. They said he is well qualified for the job and has learned from his mistakes.

"There are some matters that occurred some years ago which if they were current would be matters of concern," Committee Chairman James A. McClure (R-Idaho) said in an interview. "But I think since they are no longer current, they are not matters of concern."

"I have a strong feeling that this, graded on a scale of 1 to 10 of [Reagan's] appointees on energy, would rate pretty high," said Sen. John Melcher (D-Mont.), observing that he, too, had been arrested for drunken driving in the past. "The next person we have before us may not know anything about energy or about FERC."

The nomination was controversial as Trabandt himself -- a man praised for hard work and intelligence but known on the committee as the "prince of darkness." He was accused by staff members of misleading them and senators on bills.

"I've heard the word 'devious' used about his style . . . devious on the timing of release of information," Sen. Mark O. Hatfield (R-Ore.) said last week. "I find things like that difficult, but the pluses outweigh the minuses."

According to sources, White House counsel Fred F. Fielding questioned the nomination, but was persuaded to go along by former Interior secretary William P. Clark, for whom Trabandt became a trusted aide after leaving the Energy Committee in 1984.

Yesterday, Trabandt answered detailed questions about his drunken driving arrests in 1975 and 1981. In July 1981, he acknowledged, he was jailed by a National Park Service officer, and obtained an early arraignment through the intervention of Stephen Shipley, executive assistant to then-Interior Secretary James G. Watt, who supervised the Park Police.

Trabandt said he telephoned Shipley from jail, because he wanted to get back to the Senate to work on the budget reconciliation agreement. He said Shipley came to D.C. Superior Court, expedited the release and drove him to work. Shipley, no longer at Interior, could not be reached yesterday.

"Needless to say, this incident is a low point in my professional and personal life," Trabandt testified. "It is conduct unbecoming an officer or any senior official in public life . . . . I can assure this committee that change in fact has occurred since that night four years ago."

Trabandt also told of another July 1981 incident when he "was drinking heavily" at a staff party on Capitol Hill, and got into a fight with a subordinate over "my style of management." He added: "No blows were exchanged, though there may have been some missed swings."

Trabandt said that he no longer has a drinking problem, but acknowledged that he still drinks at times, and "there have been a few occasions in the last couple of years where I drank to excess." He said he now takes a taxi rather than driving if he drinks too much.

Late in the hearing, Trabandt displayed his knowledge of FERC matters, fielding questions on issues from price controls on natural gas to federal hydroelectric power projects in the Northwest. He said he worked 80 to 90 hours a week as committee general counsel.

Trabandt's hearing had been postponed twice, as committee members debated how to deal with a confidential FBI report documenting his personal problems. Members decided to submit written questions to McClure, who read them aloud.

Regarding Trabandt's 1981 arrest by the Park Police, McClure asked: "Did you tell [the arresting officer]: 'I wrote your budget. You can't do this to me?' Did you tell him that you were the chief counsel of the Energy Committee and that therefore an officer of the National Park Service couldn't arrest the chief counsel? Did you tell him you were going to call the White House . . . ?" Trabandt said he was too intoxicated at the time to recall.

In a lighter moment, he said of his night in jail: "I shared the cell with a gentleman who I recall was a very large man in street clothes. He and I agreed that he would sleep in the bunk and I would stand in the corner." The senators, tense through most of the hearing, broke into laughter.