The next edition of the "Plum Book" of executive-branch jobs open to political appointees will list six times as many State Department jobs as in the past, to the consternation of career Foreign Service officers who fear that their jobs will be "up for grabs" after Jan. 20.

But staff members of the Senate Governmental Affairs Committee said members of both parties agreed to increase the number of jobs listed in the book, "Policy and Supporting Positions," across the government out of a desire for accuracy and to make the perennial patronage manual more useful to the next administration.

State Department officials said at the direction of the Senate committee and the Office of Personnel Management, 2,200 to 2,500 agency jobs will be listed this year, compared with 394 in the 1980 volume. The new posts include regional directors and many "country desk" chiefs for important nations, as well as the No. 2 and No. 3 posts in many U.S. embassies.

In the U.S. Information Agency, according to a source familiar with the plans, 575 positions will be listed, compared with only 24 jobs four years ago.

"Why bother to produce something the size of the telephone book if there is no intention to put political people into these positions?" asked Dennis K. Hays, president of the American Foreign Service Organization, the labor union of the Foreign Service.

Acknowledging that the legal status of the jobs does not change simply because they were listed in the book, Hays said, "We may be a little gun-shy but we think this sends the wrong signal to a lot of people, saying these jobs are up for grabs."

Hays said his organization has protested to the State Department, and is preparing a letter making much the same point to Sens. William V. Roth Jr. (R-Del.) and Thomas F. Eagleton (D-Mo.), the chairman and ranking Democrat of the Governmental Affairs Committee. Publication of the manual rotates between Senate and House committees, and this year it is the turn of the Republican-dominated Senate.

Roth and Eagleton approved the changes in a Sept. 10 letter to Director Donald J. Devine of OPM, which had suggested a slightly less sweeping set of guidelines to the committee July 12.

Among the major changes to the book this year are:

* A list of all 3,500 general and non-career positions of the Senior Executive Service. Under law, only about 700 of these jobs can be filled by non-career people, but committee aides said printing all the posts will give the new administration a better understanding of its options.

* A list of the entire Senior Foreign Service, which includes more than 600 job-holders worldwide. Under law, no more than 5 percent can be non-career officials, but committee aides said the listing will give a new president more leeway. * Addition of the entire O-1 rank of top State Department, USIA and Agency for International Development officials on the ground that, by law, they are exempted from the usual Civil Service rules. This group holds 1,500 jobs in State alone, of which only 25 or so are held by non-career officials.

There is no legal limit on the number of O-1 jobs that could be filled politically, though both tradition and the specialities involved make it difficult do so. Senate aides said they all should be listed because they are theoretically available for presidential appointees.