It was a warm and cordial letter, admittedly a computer creation, but warm and cordial nonetheless, from the National Rifle Association.

It was signed by Harlon B. Carter, NRA's executive vice president, and it was sent to Orvel (Duke) Simmons, who lives on the outskirts of Marquette, Mich.

"Because NRA has already been working for you, and because you have missed out on the many important NRA membership benefits," Carter wrote, "I've taken the liberty of putting your name on our temporary membership rolls. . . "

Orvel (Duke) Simmons didn't quite know what to make of it. But, then it wasn't much more puzzling than other communications he said he'd had before from the NRA.

Simmons is a resident of the Michigan state prison at Marquette. He is serving three life terms for murder, plus some 60 more years for other assorted crimes.

"It does strike me as macabre that NRA would seek support for its existence from such as I," Simmons recently wrote a friend in the Washington area, Simmons, also an artist, sent along a cartoon in which he depicted himself as a convict tearfully touched by NRA's appeal.

The NRA, of course, is the country's leading opponent of gun-control legislation. And it claims its rolls are not open to anyone convicted of a crime of violence.

But because "our strength is in numbers," as NRA public affairs director Lee Jorgensen puts it, the organization is in the midst of a direct mail membership drive.

NRA's aim in Project 2 Million is to boost its membership to that level from its present 1.1 million, he told a reporter. To do that, computerized mailing plays a key role.

So it did not strike Jorgensen as macabre, humorous-or even implausible-that Prisoner No. 83272 at the Marquette prison might have received a "Dear Member-elect" letter from Carter.

"We are in a direct-mail phase and mailing lists are leased from different organizations. He could be on a magazine subscription list. Or his name could have been sent to us a prank. Or he could have done so himself by answering one of the ads we have placed in magazines," Jorgensen said.

That may explain Carter's latest letter to Duke Simmons, but but it doesn't explain the Michigan prisoner's earlier dealing with NRA.

Simmons said he and an inmate-friend several years ago designed and silk-screened about 200 emblem patches for the pistol team at the state prison in Jackson, Mich.

The pistol team, by the way, is not for inmates. The security guards at Michigan prisons practice their marksmanship by holding competitive shooting matches.

After designing the patches for the Jackson team, Simmons said, "We were given certificates of appreciation by the NRA, who are big on impressive-looking certificates and documents. They require that to become a card-carrying member you subscribe to American Rifleman or some other shooter's rag and state that you have never been convicted of a crime of violence."

"They enclose a note saying, "Would appreciated your passing our membership information and application on to your shooting and hunting friends." It's not the first time they have wrote and in fact sent me some fired up computer cards asking questions with boxes to mark concerning how I felt about confiscation of small arms."

Jorgensen allowed that it is conceivable that a convicted felon could become an NRA member, despite the group's efforts to keep them out. Applicants are asked to "certify" that they do not have criminal records, but beyond that, double checking is difficult.

One of the NRA's chief philosophical opponents, Handgun Control Inc., formerly the National Council to Control Handguns, thinks the NRA's direct-mail appeals reveal a dark side of the larger debate.

Council director Nelson T. (Pete) Shields said, "They claim to want no controls, but just put the criminals in jail, yet here they are complimenting people who are murderers who may be good gun advocates. It fits their image-nice words of Americanism and flag-waving, but it's really guns for the sake of guns, period."

Convict Simons may be on NRA's mailing lists and he may be solicited for membership, but there's one thing he will not get at Marquette prison-copies of the NRA magazine.

"We don't permit their magazine into the prison," said Paul Maynard, assistant to the warden. "It sometimes contains schematic drawings of fire arms, trigger devices, and we think this could help someone here figure out how to make homemade guns. We don't need that." CAPTION: Illustration, Convict Simmons, also an artist, drew a sketch showing his reaction to NRA appeal