A candidate for a federal judgeship in Colorado, whose nomination has been mired for 11 months in a dispute about whether he was candid in filling out his Senate Judiciary Committee questionnaire, has withdrawn his name from consideration.

Robert N. Miller, the U.S. attorney in Denver, asked President Reagan recently to withdraw his nomination to become a federal trial judge in Denver. Miller, 47, was nominated Feb. 5 to fill a seat that has been vacant for 3 1/2 years, since July 1984.

"I just got tired, I guess, and tired of all the politics involved," Miller said in a telephone interview. "I just feel like the process is a grinding one and I just guess I wasn't up to lasting that long."

Like all nominees for federal judgeships, Miller was required to fill out a Senate Judiciary Committee questionnaire that inquired whether he had ever been "disciplined or cited for a breach of ethics or unprofessional conduct."

Miller said no -- an answer that, in hindsight, doomed his chances of becoming a federal judge, drawing the ire not only of Democratic members but of Sen. Strom Thurmond (R-S.C.), the committee's ranking Republican.

A background check disclosed that Attorney General William French Smith, in September 1984, had sent Miller a letter of reprimand.

The letter, hand-delivered to Miller's home by a Justice Department official who flew to Colorado from Washington, criticized the U.S. attorney for refusing to sign an indictment of a paving company in a bid-rigging case and then telling a newspaper reporter that he declined to sign the indictment -- the customary practice in that office -- because he thought the case was "unprosecutable." The Justice Department later lost the case.

"Your conduct has reflected adversely upon yourself and the Department of Justice and has raised questions as to whether you possess the good judgment required by the position of trust you hold," Smith wrote.

The saga of Miller's failed bid to become a federal judge is also a tale of what can happen to a nominee, unskilled in the ways of Washington, who hits unexpectedly unfriendly fire -- and does not have an ally willing to shield him.

Miller was nominated only after the seat had been vacant for more than 2 1/2 years, and the Justice Department had rejected Colorado Sen. William L. Armstrong's first choice, Denver lawyer Carol Welch, according to Justice Department and congressional sources. The Denver Post reported that, in her Justice Department interview, Welch said she was personally opposed to abortion but believed the government should not interfere with a woman's decision to have an abortion.

Although Armstrong intervened to prevent the Judiciary Committee from sending back Miller's nomination during the August recess, a move that would have required Reagan to renominate Miller, committee sources said they did not perceive Armstrong -- who as the state's senior senator and only Republican would normally play a pivotal role in picking judges -- doing much on Miller's behalf.

"When a senator's supporting these nominees, we know about it," said a committee aide. "You hear from these guys." That did not happen with Miller, the aide said. Armstrong's office declined to comment.

"He did not have a home state senator banging away," said a Justice Department official. "Armstrong did go to bat for him but it was clear he was not Armstrong's choice."

The lead role in defense of Miller was played by Rep. Hank Brown (R-Colo.), who assembled a thick folder about the nominee that some committee aides compared to briefing books prepared in support of Supreme Court nominee Robert H. Bork. But Brown did not have the necessary clout on the other side of Capitol Hill.

Meanwhile, the Justice Department found itself forced to explain why it had chosen to nominate someone whom it had disciplined a few years earlier, and to defend Miller's failure to disclose the reprimand. In the view of some critics, it failed to defend him strongly.

"He was not the candidate we walked into the {White House judicial selection} meeting with," said one department official familiar with the nomination.

Although the Miller nomination was not expected to be controversial, with no opposition on ideological grounds, it snagged on his answer to the committee's questionnaire, and remained stuck.

In April, a little more than two months after Miller was nominated, the committee asked the Justice Department for an explanation, demanding access to internal department documents about the letter. Justice did not turn over its files until six months later -- a delay Assistant Attorney General Stephen J. Markman attributed to a failure in communications.

"They left him twisting slowly in the wind," one congressional aide complained about the Justice Department.

Justice Department officials say they did the best they could with a nomination that quickly became unwinnable after Miller failed to disclose the reprimand and then, in conversations with Thurmond's staff, allegedly made statements suggesting that he did not expect them to discover the reprimand.

"Miller shot himself in the foot . . . . He just did himself in by the way he handled the committee," one department official said. "Here's some poor guy sitting out in Denver thinking this is just about the best thing that has ever happened to him in his life and he kicks it away."

The official defended the department's efforts to secure Miller's confirmation. "He was probably brain-dead at that point {that he angered Thurmond's staff} but we continued to press" for a hearing, he said.

In November, nine months after he was nominated, Miller made his first appearance before the Judiciary Committee. Sen. Patrick J. Leahy (D-Vt.), who handles judicial screening for the committee, and Thurmond grilled him about the failure to disclose the letter and other incidents.

"This is not the sort of chatty, bread-and-butter letter one gets back and forth," Leahy said. "Maybe you practice law differently than where I come from and maybe technically, if it does not say 'this is an official reprimand,' it may not be, but how does the average person read that any other way than a reprimand?"

Miller said he did not disclose the letter because he viewed it as "an administrative rebuke that had been the result of some internal Department of Justice politics . . . . I thought I was reprimanded, but I did not think it was an official reprimand."

In fact, Miller said, Smith later assured him that the letter was "no big deal" and that it would not interfere with his becoming a judge.

Then Thurmond, who normally supports administration nominees, waded into the fray. "When my staff questioned you about why you had failed to tell the committee about the reprimand, you said that the attorney general had told you that it would not be in your file . . . , " Thurmond said. "Mr. Miller, from this statement, how can anyone draw a conclusion other than to say that you intentionally withheld information on the reprimand from the committee because you did not think we would find out about it?"

"Senator, I knew just the opposite," Miller said, noting that he knew the letter would be in the Justice Department files and "was not a very closely held secret where I live."

Then it was Markman's turn to explain the Justice Department's position.

"Senator, the letter was clearly a reprimand, in its own terms it was a reprimand," Markman conceded to Leahy. However, he said, the question was ambiguous and "it is our position that Mr. Miller's position is not outside the bounds of reasonableness."

Of the reprimand itself, he said, "we think his strengths far outweigh that incident."

But with Thurmond set against Miller and questions raised about a number of other matters involving him, it was clear when Congress recessed in December that he had no chance of becoming a judge.

"This protracted process has been an agonizing and distracting odyssey for me, my family, friends and office," Miller wrote to Reagan. "I respectfully request that my nomination to the U.S. District Court for the District of Colorado be withdrawn so that I can get on with my life and my job."