The Reagan administration is developing a controversial new stragegy toward Central America and the Caribbean in an attempt to demonstrate that it is not locked into a one-track military approach to such regional problems as the civil war in El Salvador.

This evolving new "Caribbean basin" policy stems from the administration's announced intention to "draw the line" against communist expansion in the hemisphere. But its backers see it as a way to overcome suspicions of President Reagan's Salvador policy -- a broader focus that will address not only U.S. security concerns but also such Third World interests as trade and development aid.

As one senior official closely involved in the process concedes, "We haven't done a very good job so far in getting across the reasons why we went into El Salvador or what we're trying to accomplish there and elsewhere in the region. It's our hope that this policy approach will give the world a clearer picture of where the dangers in the hemisphere really come from and what the intentions of this administration really are."

But the policy also has implications beyond the Caribbean. It is intended as a working-model application of Secretary of State Alexander M. Haig Jr.'s view that the United States and its allies must join in a "global approach" demonstrating to the Third World that its development hopes can best be served by cooperating with the West rather than the Soviet Union and its satellites.

In the administration's first concerted attempt to translate this idea into reality, the State Department is mapping plans to treat the so-called Caribbean basin -- Central America, the islands of the Caribbean and the northern tier of South America -- as a single entity in terms of political, economic and security ties with the United States and other major aid-giving countries willing to cooperate.

State Department officials say the plan almost certainly will include extending certain trade preferences to the area, beefing up the role of the Overseas Private Investment Corp. in underwriting U.S. firms willing to go into the region, and seeking to enlist area nations in regional self-defense schemes.

On the surface, the policy looks suspiciously like one of those quadrennial rediscoveries by a new administration. One of the first foreign policy intiatives of the Carter administration four years ago was to launch, with much fanfare, a program of priority attention for the Caribbean basin. The idea was shelved as unworkable roughly two years later.

This time, however, there appears to be a difference. As one State Department official who has worked on both approaches puts it, "The Carter administration got involved with the region out of a sense of well-intentioned but vaguely focused altruism. The Reagan people are motivated primarily by fear -- a genuine, deeply felt fear that the Cubans, and behind them the Russians, will be coming across our southern borders if we don't involve ourselves aggressively in the area."

The difference has caused disagreement among those officials charged with drawing up the specifics of the policy. Its most enthusiastic backers, who are part of the circle around Haig, are pressing to bring the plan quickly before the National Security Council in hopes of getting it blessed by Reagan with much public fanfare.

But other officials, drawn largely from the State Department's "old latin America hands," believe it would be wiser to proceed much more cautiously. In their view, many democratic governments in the region are likely to view the policy as sugarcoating to make more palatable the Reagan administration's plans for strengthening its ties with the area's rightist military regimes.

To overcome those suspicions, these officials argue, the "Caribbean basin approach" should be pursued in a low-key manner. Indeed, they would like to softpedal the United States' initiative in the policy by enlisting the region's more influential democracies -- such as Venezuela and Mexico -- to take over the lead role in public.

Many officials, well-versed in the history of past U.S. initiatives toward the area, also believe the administration has picked the wrong place for a demonstration of the virtues of a regional approach. A "Caribbean basin" policy, they believe, might look tempting to a novice glancing at a map but will fall apart in practice.

Specifically, they say, the political and cultural differences between the largely black, English-speaking Caribbean islands and the mixed Spanish-Indian societies of Central America outweigh their geographic proximity. One official says bluntly, "Anybody who went through the Carter administration efforts or earlier false starts knows that it's like trying to mix oil and water."

The experiences of the Carter and other administrations were brushed aside, the skeptics of the new policy say, partly because the administration wanted a policy to fit its view of East-West rivalries in the hemisphere and partly because of the lack of knowledge about Latin America evident among such ranking State Department officials as Haig, Deputy Secretary of State William Clark, Counselor Robert C. MacFarlane and Thomas O. Enders, the assistant secretary-designate for inter-American affairs.

Enders, principally responsible for overseeing the policy's evolution, is an aloof, hard-driving career officer who is regarded as a top-drawer economic expert but who has no experience or background in Latin America. Partly for that reason, he has kept such a low profile as to raise questions about whether the Bureau of Inter-American Affairs has become "an annex of the Pentagon" -- a reference to the apparent heavy influence of Haig's designated ambassador-at-large, retired Army Lt. Gen. Vernon Walters, and other former officers in key jobs at State and within the NSC.

However, sources familiar with the situation, while acknowledging that Walters has clout with Haig, insist that Enders is tough and talented. One characterized him as among "the nastiest and brightest" of senior foreign service officers, whose lack of visibility has partly resulted from his absorption in drafting the Caribbean basin policy and in restructuring his department to administer it.

The sources add that Enders has come to recognize that many of the doubts about the policy's viability are valid, but they stress that doesn't mean the policy will be abandoned; it has too many influential partisans for that to happen.

Officials involved in the policy-making process say that while it will continue to carry the "Caribbean basin" tag, plans for its implementation are being broken down into what one bureaucratically calls "two separate subregional approaches, one for Central America and one for the Caribbean islands, with a few interlaces as philosophical justification for the title."

However, this internal tinkering inevitably is going to run counter to the view of the policy as a way to expose what is considered the threat of Cuban-inspired communism and rationalize the militant stance Reagan has taken toward it.