Sen. William Proxmire (D-Wis.) charged yesterday on nationally televised "Face the Nation" that Attonrney General Benjamin R. Civiletti, while "a man of integrity and decency and honor," cannot be expected to conduct "the right kind of investigation" of his "buddy" in President Carter's cabinet, Treasury Secretary G. William Miller.

"I think the Justice Department is biased, overwhelming biased," Proxmire, chairman of the Senate Banking, Housing and Urban Affairs Committee, alleged on the CBS network program, carried locally by WDVM. "They have a massive conflict of interest."

Proxmire condemmed Civiletti's refusal to appoint a special prosecutor to find out if Miller perjured himself in giving "false and misleading" sworn testimony at committee hearings about a dozen bribes paid for foreign sales by Textron-Bell Helicopter.

The company is a division of Textron, Inc. which Miller headed before coming to Washington. The hearings were on his first appointment, to head the Federal Reserve System.

Miller denied that he knew of any bribes. In one case, involving a $300,000 payment, Miller told the committee he would look into it and then reported that the payment was not a bribe. "We now know that it was a bribe," Proxmire said.

Proxmire told the nation-wide television audience of a Jan. 24 letter in which Deputy Assistant Attorney General John C. Kennedy told him that an investigation by the Criminal Division into possible perjury at the hearings -- at which several persons testified -- may not be completed for "several more months."

Only after "certain international investigative steps" have been taken will the department "be in a position to evaluate the merits of the case," Kennedy wrote. The letter had surfaced at a committee hearing Friday, but eluded notice.

Proxmire protested that Civiletti "cleared" Miller even though the investigation, which the senator had requested, is incomplete, and even though there is a "strong indication" that Miller "may have known" some of his sworn statements were "lies."

Civiletti's clearance came only 48 hours after the Securties and Exchange Commission had revealed the bribes.

A Justice Department spokesman rejected Proxmire's conflict-of-interest charge, pointing out that it was Congress that entrusted the attorney general with the responsibility for deciding whether to name a special prosecutor to investigate allegations made against officials up to and including the president.

As to the Criminal Division's investigation, the spokesman said it has produced "no evidence to implicate Miller in any violation." He said that a number of witnesses have been interviewed, that some of them have been granted immunity from prosecution, and that the investigation is continuing both in the United States and abroad.

Proxmire, citing Miller's "lifetime record of honest and decency," said-that the appointment of a special prosecutor is in the interest of the secretary and the administration.

"It shouldn't be left hanging like this," Proxmire said. "I would hope the president. . . would say he wants an objective investigation. I wish Mr. tMiller would take that position."

Proxmire emphasized that 11 senior Textron officials suspected of having knowledge of bribes and invoked the constitutional protection against self-incrimination at committee hearings. A vigorous investigation is needed to find out whether they had communicated with Miller, Proxmire said.