The Senate Banking Committee finally agreed yesterday to vote - on Thursday - on the nomination of G. William Miller to head the Federal Reserve Board.

All sides expect the committee and the full Senate to approve his nomination.

The committee's decision came after Miller made a second appearance to defend his record and integrity as chairman of Textron Corp. - an appearance during with Chairman William Proxmire (D-Wis.) urged Miller voluntarily to withdraw his name.

Miller heatedly refused, and several times clashed with Proxmire, his leading and perhaps only opponent on the committee.

Action on Miller's nomination has been held up for five weeks while the committee investigated whether Miller or Textron bribed the head of the Iranian air force to win a $500 milliion helicopter contract in 1973.

Miller reappeared yesterday - five weeks to the day after his first confirmation hearing - to repeat categorical denials that he or his company paid a bribe to the late Gen. Mohammed Khatemi through a company the general silently controlled.

"The facts ring loud and clear, Mr. Miller," Proxmire charged yesterday. "Textron bribed Gen. Khatemi."

"Senator, everything you've said I disagree with," Miller shot back. Miller said that he was not convinced that Khatemi secretly owned Air Taxi Inc., Textron's Bell Helicopter sales representative in Iran until Bell paid $2.9 million to Air Taxi in 1973 to cancel the sales agreement.

One-by-one Democratic and Republican members of the committee declared that the staff investigation (it included three volumes of documentation) and committee interrogation of several Textron and Bell officials failed to link Miller, Textron or Bell to any improper payment in Iran.

"You haven't laid a glove on him," an angry Sen. Thomas J. McIntyre (D-N.H.) told proxmire. "It's important to get this man on the job."

The Securities and Exchange Commission has announced its own investigation of several Textron activities that could be questionable or illegal, including overbilling, underbilling and promotional practices by some of Textron's 30 divisions.

Miller told ranking minority member Edward W. Brooke (R-Mass.) that he has looked into each of the SEC's charges and so far has turned up no evidence of any wrongdoing, although he conceded the SEC's list includes some practices he disapproves of and has ordered stopped. One of the allegations, he said, involved documents fored b ya disgruntled employe who had been fired.

Proxmire told Miller that because the SEC investigation could take four to six months - and because a cloud will hang over Miller no matter what the SEC decides - the Textron chairman should voluntarily withdraw his nomination before the Banking Committee vote Thursday, a vote Proxmire freely admitted Miller would win easily.

Brooke, who with Proxmire had been a major force behind the investigation of Bell Helicopter's relationship with the Iranian general (who died in a hang glider accident in 1975), disagreed with Proxmire. Brooke said he was satisfied Miller had told the truth and was prepared to vote for him.

"Take 48 hours to think it over," Proxmire admonished Miller.He said the Federal Reserve, the nation's central bank, is a most sensitive agency that should not have a cloud over it.

"I don't need 48 hours," Miller replied. "In my conscience there is no question that any investigation will uncover any wrongdoing on my part or question my integrity."

Miller told Proxmire that withdrawing from the nomination "is the most irresponsible thing I could possibly do - to this committee, to Congress, to the Federal Reserve, to the president, to the nation and to myself and my wife, Ariadna."

Democratic members of the committee, who had voted for the probe when the Central Intelligence Agency told the committee that Bell Helicopter had made a large payment to a firm silently controlled by Gen. Khatemi, had become restless as the investigation dragged on without turning up any convincing evidence that Miller or other top Bell and Textron officials knew of Khatemi's role.