Frank M. Lewis opted for early retirement at 55.

John P. Schmidt got a taste of power -- for all of six days.

Alan Pollock, meanwhile, had to call a meeting to discuss how to answer the telephones.

They are among the last of the employes of the Civil Aeronautics Board, people who are going about the business of going out of business.

As a result of a law Congress passed six years ago, at 5 p.m. today the CAB will do what government agencies rarely do: shut down.

Most of the CAB's functions, and 313 of its workers, will be swallowed up by the mammoth Transportation Department in the Nassif Building across town. While some of the agency's functions will continue, the CAB will lose not only its name, but the characteristics that made it distinct: its small size and its independence from the White House.

Those changes, more than any others, account for the mixed emotions with which CAB workers greeted the move. Said chief librarian Mary Louise Ransom: "This is like a mom-and-pop operation compared to the bureaucracy there at DOT. Everyone's afraid that it could get political."

"This is a very small agency," said Myrna Adams, who heads the dockets section. "Everybody knows everybody else. DOT is a whole different world. It's like living in a small town and moving to the big city."

"I'll have to start wearing more comfortable shoes," she added. "Those are long halls over at DOT."

Frank Lewis, who had been chief of the financial and cost analysis division, chose to retire Dec. 22 instead of accepting a transfer. "This is a small agency," he said as he packed up his office last week. "It was only 800 people at the very top. If you've ever been over to DOT, that's an entire city block. That's big government over there.

"Someone once said of the CAB that it was one of the only agencies in Washington you could really manage," he added. "Because we weren't big enough, you didn't have all those layers of management. Here, everybody knows everybody else. Everyone here now was here six years ago."

When Lewis retired, his assistant John Schmidt got a quick promotion to acting chief of the division. Schmidt got to preside over the packing of filing cabinets and the labeling of boxes to move the seven-person office into DOT's larger financial analysis section. "My acting chiefship lasts a total of six days," he noted.

"We're looking forward to it," Schmidt said of the move. "We've gotten good feelings from the people we've talked to over there. They want us and they'll put us to use."

Schmidt's comments reflected the conflicting emotions of most of the CAB workers who are left: the fear of losing their independence is tempered by the feeling of relief that after months of uncertainty, a new job is waiting. "After the roller coaster of emotions that we've been through," said Alan Pollock, who heads the public affairs office, "a lot of us are just looking forward to getting over there and into a healthy organization."

"Three months ago, a lot of people didn't know if they were being transferred," said Wallace Stefany, who also works in the public affairs office. "There was a gloom-and-doom feeling. Not knowing is worse than knowing something bad."

The demise of the 46-year-old agency reflects a historic shift from the days of tight federal control over the airline industry, with the government regulating everything from routes and fares to the number of flights, to the current competitive atmosphere that has produced new low-cost fares and no-frills airlines. The shift was institutionalized by the 1978 Airline Deregulation Act.

The CAB reached a peak of 830 workers in 1979, but since then, has been phasing out functions, finally surrendering control over airline fares last year. As if to symbolize the agency's decline in status, electricity in some offices is still supplied by bulky yellow electrical cables running over the carpeting, after a flood nine months ago caused a blackout and no one bothered to repair the power lines.

Now the Connecticut Avenue office building that houses the CAB is sporting a sign that broadcasts the agency's fate: "Lease -- 146,000 Square Feet -- Top Six Floors." And the economists and auditors and lawyers who once controlled the growth of the nation's airline industry are now trying to close their remaining cases between packing their books and files into brown pasteboard boxes.

Myrna Adams needed 424 boxes to pack all the papers in her docket room -- one case alone accommodated 120 blue binders. The hard part, she fears, is not getting it all moved, but putting everything back in chronological order. "We have a lot more work to do," she sighed last week. "We may not get it all done in time."

Ransom is busy disassembling her library. Some of the books are being given to other agencies, and officials from the Justice and Housing and Urban Development departments swept in like vultures to make off with many of the agency's metal bookshelves. Ransom is going to become a reference librarian at the Federal Aviation Administration.

Other agencies have closed before. But Pollock cannot remember one that was around for so long or had been as important a part of the federal regulatory structure as the CAB.

Most of the CAB offices -- including Pollock's, the general counsel's staff, Adams' docket room and Schmidt's cost analysis branch -- will not move until Friday.

Last Thursday, Pollock and his staff held a "sunset luncheon" to discuss, among other things, how to answer the telephones after the close of business today, when the agency, on paper, ceases to exist. Suggestions ranged from "DOT annex office" to "CAB Sunset Office."

But at last the group arrived at a solution in keeping with its new status as a mere cog in the bureaucratic machinery of DOT. "We don't have to decide anything anymore," Pollock said the group concluded. "Now we can just wait for someone to tell us."