President Reagan's Caribbean basin development plan attracted broad, bipartisan support yesterday, but congressional sources warned of trouble on Capitol Hill because of reluctance to vote large sums for foreign aid when deep cuts are being made in domestic spending.

In addition, congressional liberals, while praising those aspects of the plan aimed at combating poverty in the Caribbean region, expressed concern at Reagan's insistence on relating the program to his controversial El Salvador policy and his ideological preachments against communist Cuban influence in the hemisphere.

The net effect was to leave unclear, for the moment, the prospects for congressional approval of the plan to aid Central America and the Caribbean islands through a combination of trade preferences, incentives for foreign investment and increased financial assistance.

Of most immediate concern to backers was how Congress will react to the president's proposal to increase economic aid to the region by $350 million in fiscal 1982 and then to seek $664.4 million in fiscal 1983 appropriations. Complicating the situation is Reagan's intention to ask Congress to approve an additional $60 million in military assistance, with more than half of it earmarked for El Salvador.

Typical of the mixed emotions stirred by the Caribbean plan was the reaction of House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.). He said: "I truly believe the president is on the right road . . . . I would think on the economic part there would be those out there opposing it because of economic conditions in the United States, but I think it would pass the House."

However, O'Neill repeated the call he made earlier this week for Reagan to hold back any additional military aid for the military-civilian government in El Salvador until after March 28 elections for a constituent assembly give a better picture of whether that Central American country is on the road to a democratic system that can attract popular support.

Rep. Clement J. Zablocki (D-Wis.), chairman of the House Foreign Affairs Committee, said "those who see this as 'a Marshall Plan for the Caribbean' will be sorely disappointed. Neither the magnitude of U.S. assistance nor the local economic base are present to reproduce the miracle of the Marshall Plan."

(Named for a former Army general and secretary of state, George C. Marshall, this provided billions in financial aid to postwar Europe in the late 1940s and was credited with restraining the expansion of communism.)

Still, Zablocki added, "it is an important step, and I would hope it would be supported by the Congress."

House Minority Leader Robert H. Michel (R-Ill.), agreeing with his Democratic colleagues, said: "There's no question that domestic economic considerations will enter into our debate. I can only hope we keep matters in perspective by keeping our economy and our international interests in mind."

The chairman of the House subcommittee on inter-American affairs, Rep. Michael D. Barnes (D-Md.), who is critical of administration policy in El Salvador but supportive of economic aid to the region, suggested that if Reagan wants to line up the requisite congressional backing, he should stop identifying the Caribbean initiative with the Salvadoran civil war and instead call it "the anti-illegal immigration program." That was a semi-facetious reference to the administration's contention that reversing Caribbean poverty will help end the influx of immigrants plaguing many states such as Florida.

In the Senate, the chairman of the Foreign Relations Committee, Charles H. Percy (R-Ill.), another enthusiastic supporter of the plan, predicted "strong bipartisan support." But three of the committee members--Alan Cranston (D-Calif.), Christopher J. Dodd (D-Conn.) and Larry Pressler (R-S.D.)--forecast a potentially stormy passage. Both Dodd and Pressler, warning that the reaction from their austerity-pinched constituents was likely to be hostile, said enactment will require a high degree of commitment and lobbying by the president. Dodd and Cranston also took pains to draw a distinction between their support of the program's poverty-alleviating features and their reservations about the El Salvador situation.

In an echo of the ideological questions provoked by the administration's approach, Otto Reich, assistant administrator for Latin America of the Agency for International Development, told a Senate subcommittee yesterday that Nicaragua, whose leftist government is regarded by the administration as a Cuban client, will not be allowed to benefit from the program unless it changes its foreign and domestic policies.

Elliott Abrams, assistant secretary of state for human rights, making a separate congressional appearance, accused the Nicaraguan government of a "barbaric and vicious" campaign, including killing and burning, against Indian communities in that country. Reagan made similar charges in his speech outlining the Caribbean initiative.