Five Central American foreign ministers wound up a three-day peace conference here unable to agree on any concrete steps to prevent the region's growing tensions from exploding into war.

The gathering, sponsored by the Contadora group of Mexico, Colombia, Venezuela and Panama whose foreign ministers also participated, issued a communique saying that it had generated "a new phase in the process of reducing tensions." It scheduled another round of talks in Panama for mid-August to pursue what the communique called "a fluid dialogue and clear political will."

But the document also acknowledged major differences within Central America--between Nicaragua, on one side, and Honduras, El Salvador, Guatemala and Costa Rica, on the other--about what the countries of the region should do to bring peace. The Contadora group of Latin American countries outside Central America proper was formed to defuse the threat of guerrilla warfare in Nicaragua and El Salvador expanding into a broader conflict between the Cuban-backed government of Nicaragua and the U.S.-backed forces of Honduras.

But the three days of intense consultations here among the nine foreign ministers seemed to leave the isthmus as close as ever to the dangerous situation toward which it has been slipping steadily during the past year.

As if to underscore the lack of progress here, Nicaragua charged last night that a plane from Honduras had rocketed an island off the Nicaraguan port of Corinto, where Washington recently accused the Sandinista government of unloading arms shipments from Soviet-allied countries.

Foreign Minister Juan Jose Amado Tercero of Panama, presenting the communique, declared that all nine participating ministers endorsed an appeal issued by the four Contadora presidents July 17 after a summit conference in Cancun, Mexico. This 10-point program included a call for removal of foreign military advisers from the region and a halt to arms shipments from one country to another.

The United States has accused Nicaragua of shipping arms to leftist insurgents in El Salvador, while Nicaragua says the United States is arming rebels fighting to overthrow the Sandinista government.

The Cancun appeal also was endorsed by President Fidel Castro of Cuba in statements on U.S. television yesterday and by President Reagan in a letter to the four Contadora presidents last week. But Amado said these expressions of support from key opposing outside powers were not discussed in the talks here, underlining the gap between declarations of principle and military actions that he acknowedged could soon make the diplomatic efforts meaningless.

"The speed of this military action is certainly faster than the process we are using today," he said, referring to the four-nation initiative that began on Contadora Island off Panama in January.

In separate comments, Colombian Foreign Minister Rodrigo Lloreda Caicedo also underlined the distinction beween calls in principle for removal of foreign advisers and arms and the determination of opposition countries--particularly Nicaragua and Honduras--to seek military help from their allies.

"All the Central American countries agree that the foreign advisers will have to eventually go," he said. "Most of them understand it will have to be part of a general agreement." Asked if he really meant all countries, he added: "Well, to a certain extent. They say it; I don't know if they mean it."

Amado declined to explain the differences separating Nicaragua from its Central American neighbors allied with the United States.

In the past, Nicaragua has emphasized the urgency of dealing first with attacks inside Nicaragua by U.S.-backed antigovernment irregulars operating from bases in Honduras, while Honduras and El Salvador--backed by Washington--have insisted on giving priority to Cuban and Nicaraguan help for leftist guerrillas battling to overthrow the U.S.-backed government in El Salvador.

Underscoring this, Nicaraguan Foreign Minister Miguel D'Escoto charged on arrival here Thursday night that his government is participating in the Contadora talks "more or less with a pistol to our heads."

In addition to the Honduras-based guerrillas financed and organized by the U.S. Central Intelligence Agency, D'Escoto was referring to President Reagan's decision to dispatch naval task forces down each side of the isthmus and massing up to 4,000 U.S. troops for exercises in Honduras.

Previously, the four Contadora ministers have met separately or in tense circumstances with their Central American colleagues.

In previous meetings, for example, D'Escoto underlined his caution by staying away from some joint dinners. This changed in the three days of talks here, the communique said.

Amado made it clear that Reagan's suggestion of a role for the Organization of American States was not discussed. OAS officals are said to be reluctant to get their group involved in the contentious Central American standoff. But Amado said that if some accord were reached, international groups such as the OAS or the United Nations eventually could play some role in helping carry it out.