A man saying he is a defector from Argentine intelligence in Central America, speaking on a videotape shown here, has outlined in detail a complex system of clandestine connections among the Argentine military, the Honduran high command and Nicaraguan exiles seeking to overthrow their country's leftist Sandinista government.

Identifying himself as Hector Frances, of Argentina's "Intelligence Battalion 601," he names scores of alleged contacts in Central America, including one American he describes as having ties to Sen. Jesse Helms (R-N.C.). He also claims that the U.S. Central Intelligence Agency is funding these covert operations and describes a plot to kill exiled Nicaraguan hero-turned-rebel Eden Pastora and blame it on the Sandinistas.

Those parts of the tape that could be independently corroborated provide the first small but substantive clues of what was until now the virtually impenetrable Argentine connection in Central America's secret wars.

Other parts of Frances' 70-minute statement echo standard Sandinista charges about U.S.-orchestrated covert and overt aggression against Nicaragua. There are indications that Sandinista sympathizers, if not the government itself, were involved in its distribution.

Independent sources in Central America and the United States say that an Argentine named Hector Frances, living on a tourist visa in Costa Rica and known to have close ties with anti-Sandinista Nicaraguan exiles, disappeared from San Jose in an apparent kidnaping a little more than a month ago.

According to official Costa Rican sources, that country's police had been following his movements. An official said Frances was known frequently to be in possession of large sums of money that police "suspected he was receiving from his government" and that "with certain regularity, he traveled to Honduras."

Although several men struck Frances and his wife outside their house and threw Frances into a waiting van, the sources said, no one claimed responsibility for the deed and the Argentine Embassy made no representation on Frances' behalf to the Costa Rican government. His wife, they said, has left the country.

Pastora, in a telephone interview from his home in Costa Rica yesterday, confirmed knowing Frances, whom he described as "from Argentine intelligence" and working in Costa Rica with exiled Nicaraguan national guardsmen fighting the Sandinistas.

A senior member of the Nicaraguan Democratic Forces, the principal anti-Sandinista exiles, also acknowledged knowing him.

Nat Hamrick, who is named in the tape as having "ties" with Helms and "opening doors" in Washington for anti-Sandinista exile operations, was reached at his North Carolina home. Hamrick, who said he is "in the lumber business," acknowledged "knowing and liking" Helms and said he had "business" meetings with Frances and rightist Costa Ricans in San Jose. Hamrick denied any political involvement with anti-Sandinista rebels. But, he added, "I sympathize with them and I empathize with them and I hope they overthrow the bastards."

Although the Reagan administration repeatedly has declined public comment on reports that it is engaged, along with Nicaraguan exiles and other Latin American military forces, in a covert campaign to destablize the Sandinistas, numerous accounts of such activity have been published over the past year.

Last February, The Washington Post reported that the administration had authorized a broad program of political, economic and propaganda activities against the Cuban presence in Nicaragua and the alleged Sandinista supply of weapons to guerrillas fighting the U.S.-backed government in El Salvador.

A further account, published in March, said that Reagan subsequently had authorized, in December 1981, a $19 million program of indirect CIA covert operations against Nicaragua, including the buildup and funding of a 500-man Latin American paramilitary force to operate out of commando camps spread along the Nicaraguan-Honduran border.

Training for and operation of the program were to be done in conjunction with "friendly" Latin American governments.

Since then, although both governments have refused to confirm that such a program actually was put into operation, anti-Sandinista Nicaraguan exiles operating out of Honduras have claimed a growing string of successful cross-border and internal sabotage attacks against the Sandinista government.

Beyond that somewhat sketchy framework, and a steady stream of accusations launched from all sides, little has been reported.

Three weeks ago, however, two Washington Post reporters received in Washington copies of the same Frances tape shown here yesterday by the leftist Democratic Journalists' Union of Mexico.

The copies of the tape sent to the reporters came from a fictitious suburban address outside Washington. The presentation yesterday took place at the Mexico City office of the Latin American Journalists' Federation, which is headed by Danilo Aguirre, a Nicaraguan journalist active within the Sandinista movement.

The tape shows a man who fits descriptions of Frances, who identifies himself and describes how, by means of a faked kidnaping in San Jose, he defected because he hated both the United States and his old commanders in Argentina in the wake of the Falklands war.

Frances said he entered "Battallion 601" -- an identification independently known to refer to the intelligence arm of the Argentine Army -- "approximately two years ago" for training to help him evaluate and aid "counterrevolutionary forces" working out of Costa Rican territory, especially with propaganda and the development of operational "cells."

The chief of the overall Central American program in Argentina, Frances said, was named Col. Davico.

A high Honduran intelligence official also identified Davico as the head of the Argentine program. Argentine sources confirmed that Col. Mario Davico is on active duty in the Argentine Army, and U.S. sources described him as the aide to the pre-Falklands head of Army intelligence.

When the project began last year, Frances said, about 50 Nicaraguan exiles were sent to Argentina for training and subsequently dispersed in Central American and U.S. exile training camps as teachers. A senior exile source confirmed that "there have been some people in Argentina."

Frances said he began his own work on arrival in Costa Rica last year. He details names and meetings, including the ones with Hamrick and some with Pastora, as well as planned and carried-out operations. Frances describes a three-part structure, centered in Honduras, of coordinated commands among Argentines working in Central America, members of the Honduran military and exile leaders who coordinate weapons shipments into the country, operate training centers and are centered in a series of safe houses. Some, he said, are run by the CIA in Tegucigalpa.

The Argentine staff in Honduras, he said, is headed by a man he identifies as Jose Ollas, in charge of logistics, and Col. Osvaldo Riviera in charge of operations. According to Frances, this group in turn is linked to a special Honduran general staff headed by the Honduran Armed Forces commander, Gen. Gustavo Alvarez.

"With the permanent vigilance and the permanent orientation of the CIA expressing the orders of the State Department, these interrelated general staffs dominate the Nicaraguan anti-Sandinista general staff," Frances said.

Although Cuban and Nicaraguan officials have said in recent months that Argentine officers assisting the exiles in Honduras were withdrawn during the Falklands war, other informed sources have said that a group numbering about 35 Argentines remains in Central America.

Frances presented no names or details of his charges that the CIA is in charge of the various Central American intrigues he outlines. The only American he mentioned by name is Hamrick, whom he said he met with about a year ago and describes as "related to the group of Sen. Jesse Helms and also the American Intelligence Central for which he carries out multiple, fundamental activities in the Costa Rican network."

At the meeting, Frances said, were businessmen Carlos Feders and Manuel Oliveira Pinto of the right-wing Free Costa Rica Movement. Hamrick confirmed this.

The objective, Frances said, was to figure out ways to influence Costa Rican President Luis Alberto Monge, primarily through economic pressures, so that he would facilitate counterrevolutionary operations out of his country.

More recently, according to Frances, there was talk with assistants to the Costa Rican foreign minister of setting up an incident in which the Sandinistas would appear to have made attacks inside Costa Rican territory. This would serve as a pretext for Costa Rica to invite the help of foreign troops. Hamrick was supposedly "opening the doors in Washington for this maneuver."

Hamrick denied any association other than that having to do with his lumber business, which he said also operates in Central America.

Frances also charged, presenting no proof other than inference, that Pastora also received money from the CIA. Pastora, who is in a bitter feud with the ex-guard exiles, has repeatedly denied this.

It was because of Pastora's lack of ideological "definition" and refusal to link up with the others, Frances said, that plans were made to kill him. Frances said a rocket that could be launched from an automatic pistol was ordered from the 601 Battalion for this purpose and the plans called for Pastora to be killed in much the same style as former dictator Anastasio Somoza was, in order to blame the assassination on the Sandinistas.

Frances did not say why the plan was not carried out.