One of the books on the required reading list of every incoming administration is the "plum book," a blue-covered, guide to the roughly 3,000 policymaking and patronage jobs a new president must fill. But the next president-elect will have something extra to examine: already dubbed "the prune book," it will describe the 100 or so toughest jobs up for grabs.

"A prune is a plum with experience," said the author of the forthcoming volume, former State Department spokesman John H. Trattner, explaining the informal title of the forthcoming work. Unlike "the plum book," which contains only one line of type to describe each opening and its pay level, "the prune book will show in some detail what kind of personal and political credentials the toughest jobs really require," Trattner said.

The unusual volume, which will be published late next year, is the product of The Center for Excellence in Government, a 4-year-old organization of 265 "prunes" who had experience in key government or government-related executive positions and now are in private business. The center, the brainchild of Mark A. Abramson, a former career civil servant at the Department of Health and Human Services, seeks to improve the often-neglected area of management in the government.

The prune book will cover jobs that can make or break an administration, according to Abramson. It will not include Cabinet posts because these are often uniquely personal appointments by an incoming president, but is likely to concentrate on sub-Cabinet and agency director-level positions. "These really key posts require both policymaking skills and management skills . . . {and} often management gets shortchanged," Abramson said.

To identify and describe in detail the toughest executive management and policymaking jobs in Washington, 15 teams of former officials have been organized to concentrate over the summer on different departments and agencies. Each team consists of people who served in executive posts in the areas they are covering. The teams will nominate their lists of toughest jobs based of their own experiences and interviews with former Cabinet officers and others.

The aim is "to convey the wisdom and experience of people who actually have had these jobs over six administrations or more, and people in Congress, the constituencies and the press" about what is required to fill the post effectively, Trattner said. "We don't expect to turn things around overnight, but if even 10 percent of these top jobs in the next administration can be filled with this kind of information in mind, the book will have been a success."

Although the identification and selection process for the toughest jobs is only in its early stages, Abramson and Trattner in a recent interview mentioned deputy secretary of state, commissioner of the Social Security Administration and commissioner of the Food and Drug Administration as the kind of posts that are likely be be included.

Trattner, a former Foreign Service officer who once served as special assistant to the deputy secretary of state, has drawn up a six-page sample report on the responsibilities and qualifications of that job and a list of those who have held it in recent administrations.

One qualification listed is being able to work effectively with the White House -- sometimes with the president personally -- on foreign policy issues. "A lot of people freeze in dealing with the president," an unnamed former deputy secretary of state was quoted as saying. Another former occupant of the job was quoted as saying, "You have to find somebody who is adaptable and quick, who'll be able to read the secretary and instinctively know what needs to be done. You don't want somebody who immediately says, 'Well, I've got to chart an entirely new course.' He has to be able to pick it up an move it along."

For each of the toughest posts, the prune book will include "specific personal or professional background and skills needed" to do the job well. For the No. 2 man at State, these are:"Extensive background in business or law, preferably in the international area. Negotiating skills developed in either of these backgrounds is extremely useful. "Work and/or residence abroad. Knowledge of foreign language(s)."

The originators of the prune book point out that the next president and his staff will have to choose the occupants of about 3,000 jobs in the 2 1/2 months between the Nov. 8, 1988, election and his inauguration on Jan. 20, 1989. As a prospectus for the prune book put it, "The time is short and the stakes are high."