At 9 a.m., three days after he was nominated to be Ronald Reagan's secretary of state, Alexander M. Haig Jr. was ushered into a sparsely furnished room on the fifth floor of the Reagan transition team's offices on M Street NW and handed a half-inch-thick booklet labeled "sensitive."

"This is a summary of our work to date in the identification of prospective Department of State," said a cover memo from Dudley Mecum, the transition team's associate director for national security personnel.

In the pages that followed, Mecum listed the 34 top jobs in the State Department that the Reagan administration will have to fill come Jan. 20, and from four to eight persons recommended by the transition team for each job. a

Similar "lists" covering virtually every sub-Cabinet office in government have been distributed to each of Reagan's Cabinet appointees, and they have become one of the most controversial and misunderstood elements of the Reagan transition effort.

"Even people in this [transition headquarters] building are getting excited about 'the lists,'" said E. Pendleton James, the California lawyer heading Reagan's office of presidential personnel. "They really get hot about this. Everyone wants to know, 'Is my name on The List?' and 'How can I get on The List?'"

The reason for concern is understandable: Reagan, unlike some of his predecessors who left the filing of many sub-Cabinet jobs to department secretaries, has let it be known that he and his top advisers will have final say on all such appointees.

This includes 204 undersecretaries, deputy secretaries, assistant secretaries and general counsels to the 13 departments of government, plus the administrators, directors and commissioners of 52 independent agencies.

The degree of power in each position varies, but it can be considerable. So there is keen interest in -- and some politicking over -- not only who will hold the position but who will place him or her there. Congressional committee chairmen push their favorites for agencies their committees will oversee. Special-interest groups promote candidates sympathetic to their needs, and some individuals with a yen for a certain job have been active in tooting their own horns.

The mere existence of "the lists" raised immediate countroversy. Reagan, critics charged, was trying to force subordinates on unwilling Cabinet members and put an ideological stamp on the sub-Cabinet.

These fears have subsided somewhat as it has become apparent that the lists are less than they initially had appeared to be. "We're not trying to jam things down anyone's throat," James said. "We're just trying to use some good business procedures."

But there is little doubt Reagan is keeping an unusually tight rein on the sub-Cabinet process, and James defends that tactic. "These are presidential appointments, not secretarial ones. The final decision will be the president's," he said. "You've got to have a choke-hold -- a control on who staffs government."

James' office of presidential personnel is the basic choke-hold on the process. It is here that the much-discussed lists originate, and it here that the Cabinet appointees negotiate over their subordinates.

The heart of its operation is on the fifth floor of transition headquarters, in a large, open room that resembles the newsroom of a large metropolitan newspaper more than anything else.

Dozens of telephone-topped gray metal desks are arranged in rows, newsroom style. Transition team recruiters, some drawn from executive headhunting firms, sit at some desks. At others people cull the names and make recommendations for jobs.

In the middle of the room a computer operation resembles the wireroom of a newspaper. Here the names are fed into computers for future use. James' associates and specialists work in small offices, like those used by newspaper editors and columnists along the sides of the room and in adjoining corridors.

Fred Fielding, one of John Dean's deputies during the Watergate years, has one such office. He is in charge of checking into any conflict-of-interest problems of potential appointees. Keith Bulen, a former national GOP committeeman from Indiana, who is Reagan's patronage chief, has another.

Nancy Chotiner, widow of a former Nixon aide who specializes in finding women appointees, has a fourth. Melvin Bradley, a United Airlines executive, working in another such office, recruits blacks and other minorities.

The lists given Cabinet nominees were drawn from four sources: thousands of unsolicited resumes that flowed into the transition offices from individuals, members of Congress, senators, governors and special-interest groups; a group of executive headhunting firms that volunteered to make a nationwide search and came up with 1,100 names; Reagan's "Kitchen Cabinet," made up largely of wealthy friends from California, and an in-house transition team search.

The Cabinet nominees were given "raw lists," which included names and brief biographies and descriptions of the jobs open, James said. The Cabinet appointees were free to suggest additional names, and it was not until after that point that anyone was interviewed for any job.

James called in the Kitchen Cabinet last Saturday to review names of sub-Cabinet appointees. Transition spokesmen said they had not expected any appointments until after the first of the year, and some top jobs may not be filled until well into January.

Politics and ideology will play an important part in the selection process.

"Once we get down to the final choices there will be a political evaluation," James said. "We want to check people out politically, to find where they stand philosphically."

What if a closet liberal shows up in the search?

That has not happened yet, Replied James Cavanaugh, James' top deputy. "But if it did, that person's priority would diminish rapidly. Obviously, that's something we're deeply interested in. These are policy postions, after all."

Conflicts between Cabinet appointees and Reagan's transition team are probably inevitable. If a disagreement over the final choice of a sub-Cabinet member develops, it will be noted on a "decision memo" forwarded to Reagan before he makes the nomination, James said.

"I've heard gripes from people about the operation from outsiders. But we really view it as a godsend, "said David Newhall, chief of staff to Sen. Richard S. Schweiker, Reagan's choice for secretary of health and human services. "We've been impressed with the high quality of their work, and we've felt perfectly comfortable in making suggestions of our own."

"So far we've had nothing but high marks for them," Newhall added. "Of course, we haven't gotten down to the point where we make our final choices."