The Reagan administration has broken a logjam of appointments to ambassadorial posts with more than a dozen appoointments either decided upon by the White House or expected to be announced soon, according to administration.

Yesterday, the White House announced four new ambassadorial assignments, including the appointment of Maxwell M. Rabb, 70, a New York attorney who was Cabinet Secretary in the Eisenhower administration, as ambassador to Italy.

Charles H. Price II, a candy company executive and chairman of the board of the American Bank and Trust Co. of Kansas City, will be ambassador to Belgium.

Two career State Department officials, Deputy Assistant Secretary of State for Near Eastern and South Asian Affairs Jane A. Coon and Deputy Director of the U.S. International Communication Agency Charles W. Bray III, will be ambassadors to Bangladesh and Senegal, respectively.

Although it has not been announced, sources say that the White House has also chosen other career officials for key diplomatic posts, including Ronald I. Spiers, director of the State Department's bureau of intelligence and research, as ambasador to Pakistan and Harry G. Barnes, Director general of the foreign service, as ambassador to India.

These sources also report that Michael A. Armacost, a deputy assistant secretary of state in the department's East Asian bureau, will become ambassasor to Indonesia.

Armacost, an experienced official of whom Secretary of State of Alexander M. Haig Jr. is known to think highly, was notified recently that he was being moved out of his current job. The removal was reported to be part of an apparent deal with Sen. Jesse Helms (R-N.C.) to obtain the backing of some conservative senators for confirmation of Armacost's boss, John Holdridge, as State's top East Asian official.

Among the other choices either approved or expected to be approved by the White House, sources say, are appointment of Chinese-speaking career officer Arthur W. Hummel Jr. as ambassador to China and of Arthur A. Hartment, ambassador to France, as ambassador to the Soviet Union.

William Dyess, former State Department spokesman and assistant secretary spokesman and assistant secretary for public affiars, is said to be the choice as ambassador to the Netherlands, with George S. Vest, a former assistant secretary for European affairs, is said to be the new U.S. representative to the nine-nation European Economic Community.

Two other career officers, Thomas R. Pickering and Michael H. Newlin, are said to be in line to become ambassadors to Nigeria and Algeria, respectively.

Sources say that Robert P. Paganelli, the second-ranking U.S.diplomat in the embassy in Italy, will become ambassador to Syria and that Samuel W. Lewis, ambassador to Israel, and Alfred L. Atherton Jr., envoy to Egypt, reportedly will remain in their posts.

Robert Strausz-Hupe, a veteran academician and diplomat, is said to be in line for the ambassadorial assignment to Turkey, with a career officer and former ambassador to the Ivory Coast, Monteagle Stearns, said to be the choice for Greece.

Richard L. Walker, an Asian specialist from the University of South Carolina, is said to be the choice as ambassador to South Korea.

On Wednesday, the White House announced that Theordore E. Cummings, a California real estate developer, would be ambassador to Austria.

State Department officials yesterday declined to provide any confirmation on names not yet publicly announced.