"The issue," observed Joseph N. Onek, 38, a lawyer now working in the Carter White House, a man whose entire career has been devoted to "the public interest," "is not whether we will do well" in the big, cold world that he and a few thousand colleagues now must enter.

"Presumably we're going to be very well off," Onek went on, expressing apparently wellfounded confidence for the futures of the bright young people of the Carter administration. "The issue is, if we become fat, who will be lean?"

Here is a problem of our time. Once lawyers like Onek happily signed up to work for Ralph Nader for $200 a week, Onek himself was a modestly paid attorney for the Center for Law and Social Policy, a public interest outfit here, before joining the White House staff in 1977. Now he is nearly middle-aged, and his White House salary is $55,387.50 a year. He still doesn't know what he'll be doing after Jan. 20.

The transition is a spectacle for most Washingtonians, but it is a personal crisis for about 10,000 of them. In this transition season the crisis is paticularly poignant for members of Joe Onek's generation, children of the 1960s who aren't children anymore, and who have little experience outside of government or public service work.

There are dozens of 38- to 40-year-olds all over Washington in this same uncertain status. Gus Speth, the outgoing chairman of the Council on Environmental Quality, is only 38. Richard McCall, 38, is assistant secretary of state for international organization affairs; Angus C. Macbeth, 38, is deputy assistant attorney general; Walter Slocombe, 39, is deputy undersecretary of defense; Charles Stevenson, 38, is legislative aide to Sen. John C. Culver (D-Iowa); Lowell Dodge, 40, is executive and legal assistant to the chairman of the Consumer Produce Safety Commission.

All of these people came of age in the stormy 1960s, in that heady political atmosphere shaped by the civil rights revolution, the Vietnam war and the initial efforts to clean up the environment; all were eager for spots in the Carter administration, and, with the possible exception of tax lawyer Slocombe, they never made anything like as much money as they are making today as public servants.

Today, all of them are looking for work.

Some in this group accept the idea that they are going through a change in life that will be fundamental. One of them is Simon Lazarus III, 39, a lawyer and associate director of the domestic policy staff under Stuart E. Eizenstat. Lazarus worked on airline deregulation and civil service reform in the Carter administration, two successful endeavors that he found exhilarating. He knows that life in the private sector is going to be duller.

"Private profit-making was some thing one did only as long as one couldn't find something more interesting in public service," Lazarus observed, recalling his few years in the firm of Arnold & Porter here. But his perception has changed. "If someone came up now and said, 'Let's do airline deregulation and civil service reform,' I'd only think about how hard it would be."

Lawyers now in the government are more likely to be put off by the dreariness of private practice than by questions about its morality, Lazarus said. "Private practice can be trivial." But he is ready to give it another shot. "I would like to make more money. I'd like to build a base for myself that I don't really have right now . . . some kind of professional, economic security." He says 39 is not exactly the best age to be starting out again. "That's the price you pay for having played all these games all these years."

Lowell Dodge, one of Ralph Nader's early comrades in the crusade for auto safety, finds it much more difficult to contemplate a career in the private sector. He refers to joining a law firm as becoming an RFL -- a real f---ing lawyer," and he rules it out. But he admits that the combination of the election results and his 40th birthday have left him with the feeling that "I'm growing up now and need to find a niche, and do well."

Dodge has been looking around in his old bailiwick, the public interest world. "I find there are slim pickings, because I've gotten used to making more," he said. At the Consumer Product Safety Commission, Dodge has earned $50,112.50 a year. "Frankly, it's awkward for me to go back to the public interest groups and say 'OK, pay me three times as much'" as they once did.

Dodge's preferred gambit now is to establish a new public interest group devoted to reducing the dangers of fire.

Others will give up public interest work without qualms. Richard C. Holbrooke, 39, assistant secretary of state for East Asian and Pacific affairs, is "inclined towards involvement in the business world." His State Department colleague, Richard McCall, assistant secretary for international organizations, thinks he would like to "go into the private sector and get out from under this pressure for a while." McCall is thinking about working as a lobbyist.

Did the voters on Nov. 4 wipe out the progressivism that these people had adopted as their banner? They disagree about that. Joan Claybrook, administrator of the National Highway Traffic Safety Administration, said flatly, "I don't analyze the election results as a rejection of the kind of programs I've been working on. . . . The election had an awful lot more to do with inflation . . . and concern about America as a great power."

Robert G. Beckel, a White House lobbyist who ran President Carter's campaign in Texas, sees it differently. "The country clearly repudiated activist government," Beckel said in an interview. "That doesn't mean people have turned their backs on the poor, on the need for decent education and health care," he added, but he sees a need to redefine liberal goals and means, too. "There may have to be a new generation of committed progressives . . . who can carry it on in a different way," he said -- a painful thought for a man who is just 32. Beckel now plans to go back to Texas and go into business -- two of them. He'll set up shop as an ad agency and political consultant, and also get into the energy industry on the side.

To stay in Washington or get out of town? A big question. Beckel's instinct -- to get away for awhile -- is widely shared. J. Brian Atwood, 38, assistant secretary of state for congressional relations, plans to go back to his native Massachusetts, find a job in private industry and then maybe get into local politics. But his colleague McCall, who grew up in Rushville, Neb., in "The Last Picture Show" America, will stay: "I have two young sons who were born back here. I guess when that happens you begin to indentify with this area as your home. . . ."