The Reagan administration's plans to combat communist influence in the Caribbean and Central America through increased economic and military aid have become mired in turf fights, lack of cooperation and resistance from U.S. government agencies charged with giving the policy form and substance.

"For something that's supposed to be a high priority initiative, this program is pretty close to dead in the water at the moment," said one senior State Department official who declined to be identified. "It's still early in the game, but unless some drastic steps are taken to get things moving, the whole plan is in serious danger of withering away into nothing."

The new policy, approved in principle by President Reagan, is regarded by State Department advocates as potentially one of the most important attempts by the administration to assert U.S. leadership in the foreign policy arena.

But, according to administration officials involved in the planning, efforts to work out costs and details have been discouraging. The problem, these officials said, stems primarily from resistance to key aspects of the policy in such agencies as the Offices of Management and Budget (OMB), the Agency for International Development (AID), the Commerce Department and the Office of the Special Trade Representative.

Essentially, the officials expalined, this resistance is partly because of bureaucratic inertia and unwillingness to embrace new ideas. Even more, however, it appears to be rooted in interagency rivalries and reluctance of departments to make concessions that might deplete their resources or hamper their policy goals in other areas.

OMB, for example, reportedly is concerned that increases in military and economic assistance will run counter to the administration's drive for budgetary austerity; AID strongly dislikes the idea of trying to sidestep this problem by diverting aid funds to the Caribbean from other areas.

Similarly, Commerce and the trade representative's office are understood to have strong reservations about giving tariff preferences to the Caribbean and Central America on grounds it would create demands for similar tretment from other regions and cause political trouble with domestic special interest groups.

These problems are not insurmountable, officials stressed. But, they added, the negativism present in interagency discussions is so pervasive that the policy can be rescued from inertia only if Secretary of State Alexander M. Haig Jr. and other partisans make an all-out fight at the highest levels of the administration.

"It's going to take a clear and strong expression of political will to come up with a program that has some flesh on it rather than one that has been gutted," one official said. "It has to be sold at the level of the Cabinet and the president in a way that makes clear that this is what they want, and then it has to be imposed downward on the bureaucracy to make the respond."

In theory, this high-priority interest exists. Underlying this Caribbean basin" policy is the administration's desire to show it is not locked into a one track military approach to such regional problems as the civil war in El Salvador, that it is capable of a broader focus that will address not only U.S. security concerns but also such Third World interests as trade and development.

In attempting to translate this idea into reality, the State Department has mapped plans to treat the Caribbean basin -- Central America, the Caribbean islands and the northern tier of South America -- as an entity in political, economic and security ties with the United States and other major aid giving countries willing to cooperate.

In broad outline, that calls for increased and better coordinated aid, trade preferences, wooing more private investment to the area through help from the Overseas Private Investment Corp., helping to relieve the financial burden on countries saddled with high energy-import costs and seeking to enlist area nations in regional self-defense schemes.

The idea has a number of built-in problems including doubts about whether the English-speaking Caribbean and Central America are too culturally dissimilar to be treated alike, suspicions that the policy is really a propaganda exercise aimed at isolating Cuba, a feeling by some area countries they are not being consulted sufficiently by Washington and concern about whether other industrial aid giving countries and important regional nations like Mexico and Venezuela will cooperate.

Now, these problems have been compounded by the failure of the federal agencies dealing with economic questions to share the enthusiasm for the policy evident in the top reaches of the State Department and some quarters of the Pentagon.

According to the officials, sniping at the policy on economic grounds has been evident in senior policy making circles since the idea was broached, and it initially led Reagan to take a go-slow approach.

However, at a National Security Council meeting late last month, the president did give his blessing to the general outlines of the plan; Special Trade Representative William E. Brock's office was assigned the task of coordinating the interagency planning.

That move is known to have caused some misgivings in the State Department, where there are doubts about how much attention and enthusiasm Brock's people are willing to devote to the task. Some State officials feel, though, that the assignment could lead the trade representative's office away from its previous nay-saying approach and turn it into an advocate.

In the end, though, the officials say, the real test will turn on whether Haig, who has been distracted by more immediate problems elsewhere, will be willing to go to the mat for the policy with Reagan and the White House inner circle.

A sense that time might be running out was conveyed here Friday by Jamaica's conservative prime minister, Edward Seaga, whose call last year for a "Caribbean Marshall Plan" helped to stimulate administration thinking about the policy.

Seaga, who conceded the Caribbean nations also have been slow to get together and talk about such a program, warned that if anything is to come of the idea, all the countries involved, including the United States, must have a concrete plan worked out by the end of this year.