Attorney General Benjamin R. Civiletti said yesterday that he has found no grounds for appointing a special prosecutor to pursue charges that Treasury Secretary G. William Miller lied to Congress about questionable payments made by Textron Inc. when Miller headed it.

In letters to Chairman William Proxmire (D-Wis.) of the Senate Banking Committee and Republican members of the Senate Judiciary Committee, Civiletti said that a two-year-long Justice Department investigation of the Trextron payments "has not revealed evidence that Mr. Miller was informed by anyone of improper payments by Textron or Bell Helicopter [a Textron division] or that Mr. Miller learned of such payments in any other way."

In fact, Civiletti said later in the letters, "none of the assertions that Secretary Miller has committed a criminal violation has been substantiated by the investigation conducted since early 1978."

The attorney general said much the same thing at a Senate hearing last month.

In the formal responses yesterday he noted that he was barred by a technicality from moving for a special prosecutor because the matter was under investigation by the Justice Department before the triggering Ethics in Government Act was fully in effect.

Even without the technicality, he said, "I have very serious doubts that specific information sufficient to trigger the act has been developed. . . ."

Miller said through an aide yesterday that Civiletti's decision "speaks for itself." He had no further comment.

Not surprisingly, those who had called for the special prosecutor were not pleased with Civiletti's answer. Proxmire issued a short statement saying that he was disappointed there would not be an "independent" prosecutor. s

"I do not believe that a judgment by the attorney general in Secretary Miller's case can command the public respect this matter deserves," he said. "Unfortunately, all of us will now have to live with a very unhappy situation."

Sen. Bob Dole (R-Kan.), one of the Judiciary Committee members who requested the special prosecutor, said that "to fail to utilize this machinery [the ethics act] in this most obvious of circumstances renders the whole special prosecutor procedure moot."

"How ironic it is when an administration that was swept into office in the wake of Watergate cannot effectively respond to serious charges raised by one of its own regulatory agencies against one of its own Cabinet officers," Dole added.

The Securities and Exchange Commission charged on Jan. 31 that Miller was aware of a secret $600,000 slush fund that Textron used for entertaining Pentagon officials.

The SEC report also outlined $5.4 million in payments that Textron's Bell Helicopter division allegedly made to foreign officials to increase sales. Miller headed the company during the period, from 1971 to 1978.

He became head of the Federal Reserve Board in March of 1978 and took over the job as treasury secretary last August. Miller has consistently denied that he knew about the improper payments.

In his letters yesterday, Civiletti noted that the Justice Department investigation found that "there is some evidence that certain Textron and Bell Helicopter officials who reported to Mr. Miller were told of information relating to some payments."

However, Civiletti said, all but two have denied under oath that they recall being told and the other two claimed they didn't believe the information.

Civiletti also said that the Justice prosecutors had granted immunity to six lower-level Bell employes and sales agents in the grand jury investigation.

In his letter to Proxmire, Civiletti pointed out that gathering evidence in a foreign bribery case is complex and time-consuming. He said the Justice Department has sent the lead lawyer in the case to Europe in pursuit of evidence and has asked for help from four foreign governments.