The Reagan administration's proposed budget cuts call for the United States to quit the U.N. Food and Agriculture Organization and end its $49 million annual contribution to the FAO, the main international agency combatting the famine that threatens 28 African nations.

The plan to leave the FAO, a Rome-based agency to which 144 nations belong, is included in the package of proposed cuts and freezes given to Republican congressional leaders at a White House meeting yesterday. The administration already has served notice of its intention to quit the U.N. Scientific, Educational and Cultural Organization (UNESCO) at the end of the year.

Administration officials, speaking on condition that they not be identified, said the decision to leave the FAO was in response to congressional insistence that the budget cuts cover the entire range of U.S. governmental activity, including voluntary contributions to U.N. agencies.

They said the FAO was selected to be what one official called "the symbolic agency showing a cut in that category" because of a feeling within the administration and some quarters of Congress that it is too top-heavy with bureaucracy and has been susceptible to ideological influences at odds with U.S. interests. Those are essentially the same complaints the United States has made about UNESCO.

However, the officials acknowledged that U.S. problems with the FAO are of far lesser magnitude than those involving UNESCO. Some State Department officials, who requested anonymity, went further, saying that the FAO is regarded within the department as among the most effective U.N. agencies. They added that department officials who deal regularly with international food problems apparently were not consulted about the decision to quit the agency.

These officials and some congressional sources expressed bewilderment about why the FAO was chosen at a time when world attention is focused on the devastating effects of the famine in Ethiopia and elsewhere in Africa. Some speculated that the administration, anticipating widespread objections on humanitarian grounds, deliberately put the FAO on its cut list as a "bargaining chip" that it might surrender later in exchange for congressional concessions on other programs.

Under the FAO's rules, the United States must give two years' notice before it can leave, so any budget savings would not be realized until 1988. The U.S. contribution to the FAO for this fiscal year is $49.9 million, and Congress has decreed that all voluntary contributions to U.N. agencies be frozen at current levels.