President Reagan is sending too many political appointees overseas as U.S. ambassadors and the "vast majority" of them "are relatively undistinguished as public figures," the American Foreign Service Association charged yesterday.

The association, which includes 7,060 active-duty or retired State Department Foreign Service officers, said if the present trend continues the Reagan administration will wind up putting a larger proportion of non-career officers in ambassadorial posts than any administration since World War II.

"Inevitably," the association said in an unusually tough statement released yesterday, "such appointments lower the respect of foreign countries for the United States and make a mockery of the careful selection and long and varied experience which professional career officers bring to senior assignments within the service."

The government's Foreign Service, the association made clear, has "long welcomed" the assignment abroad of individuals of "real distinction" such as former ambassadors George Bush, Ellsworth Bunker, Douglas Dillon and David Bruce, and current ambassadors Mike Mansfield, Arthur Burns and Maxwell Rabb.

"It is disappointing, however, to see that almost half of this administration's ambassadorial appointments are non-career envoys, the vast majority of whom are relatively undistinguished as public figures," the statement said.

Of 81 ambassadors selected by the Reagan administration, the association said, 36, or 44 percent, have been from outside the ranks of the Foreign Service. This is the highest percentage of all administrations, dating back to World War II.

The association cites various provisions of the Foreign Service Act of 1980 to the effect that political contributions should not be a factor in such appointments and that the ambassadorial posts should "normally" be given to career officers. Yet, the statement adds, "it is obvious that the selection of political ambassadors continues to be a reward for party loyalty and campaign participation." The association cited no specific examples of objectionable appointments.

In a related development, sources say the association has also written to Richard T. Kennedy, undersecretary of state for management, expressing concern that he is holding down two jobs and implying that he is not giving enough time to his main job, which Foreign Service officers see as looking after State Department personnel and budgetary interests.

Association officials declined to discuss the letter to Kennedy, but sources say the concern is that Kennedy has also become the U.S. representative to the International Atomic Energy Agency in Vienna and that it is difficult if not impossible to do both jobs adequately.