As someone streaked with winsome modesty, former Rear Adm. Eugene Carroll makes no large claims about his voluntary decision to leave the Navy in 1980 after 37 years. His taking of permanent liberty was more an act of conviction than conscience, he says: "I just felt we weren't going to the right places or doing the right things in our security programs." He saw that a nuclear weapons drift had become a nuclear weapons rush.

From the edges, the military career of Carroll appears as the model American success story. He won campaign ribbons in three wars, commanded an aircraft carrier, served on Gen. Alexander Haig's NATO staff in Europe and, as late as August 1980, had a big-deal, flag-draped office job in the Pentagon.

Even after leaving the military, Carroll's career glinted. He was a nuclear weapons analyst for several months with a Washington defense contractor. It was a job that promised, as so many of them do in these boom times for weapon contracts, a large salary for easy work.

But since June, Carroll has been an associate director of the Center for Defense Information, where I talked with him the other morning. CDI is an established nonprofit research group that is sometimes called anti-Pentagon but which actually is a supporter of military programs -- provided they are effective, economical and justified by something more rational than envenomed rhetoric about the Soviet Union.

It was during his months as an analyst for a defense contractor that Carroll felt he was making no purposeful contribution either to his country or his own integrity. "The workload built and built," he recalls, "and again I found I was not changing anything. I was simply producing more information to support the same programs that I'd been obliged to support during active duty . . . I was working on the same side of the street. The contractor must satisfy the customer. The customer is the Department of Defense. You must produce a product which supports its interests. I wasn't sympathetic with the product we were producing: the idea that the United States needed more nuclear weapons."

In the context of government-industry relations, Carroll's gagging at his civilian job was rare. The revolving door through which retired admirals and generals slide from the Pentagon to defense contractors is so wide and well-oiled that, from 1970 to 1979, 1,455 former military employees were hired by a mere eight companies.

The figures are from "The Iron Triangle," a new report by the Council on Economic Priorities, which says of the former Pentagon workers: "The expertise brought by these individuals is not only technical but political -- information on and access to policy making that helps create a closed network in a community of shared assumptions."

As a former insider who felt trapped in that closed network, Carroll confirms what many Pentagon critics have long charged: that the laws against conflict of intertest are seldom enforced. Even then, Carroll says, punishment is mild: "Some people have had their retirement pay reduced or withheld because they were found to be in conflict. But that's a rare case."

At CDI, Carroll shares in the workload of the organization's director, former Adm. Gene La Rocque. Both lecture, write, debate and join in the group effort to supply the public with accurate information and unbiased analysis about the nation's genuine -- and not imagined -- defense needs.

It's an invaluable mission, though Carroll often finds he most needs his skills of persuasion when among those he generally agrees with. He recalls a meeting with the Catholic peace and justice commission of Baltimore: "I was trying to persuade them not to put their political capital on the line behind a nuclear freeze campaign. I don't think that's an achievable step right now. The administration . . . is determined that we aren't going to enter into any effective arms control negotiation. To talk about a nuclear freeze is to be dismissed . . . as simple-minded peaceniks."

The pacifists-are-hopelessly-naive argument leaves me unpersuaded, even as presented by someone as reflective as Carroll. But with 9,600 nuclear warheads in the U.S. arsenal, Carroll's goal remains worthy: Slow the nuclear arms race first and think later about how to turn it around. To achieve a slowdown now may mean that the world will indeed have a later.