One of the primary figures arrested this week in what the FBI says was a plot to assassinate the president of Honduras sold a large shipment of cannon-equipped armored cars last year to the Honduran government, according to sources in Honduras and Florida.

The $7 million sale, which represented an unprecedented 200-percent increase in the number of armored vehicles in the Honduran military, was made by Gerard Latchinian, a Honduran citizen and Miami-based international arms dealer, these sources said.

According to the FBI, Latchinian, 46, frequently boasted to an undercover agent that he could supply whatever weapons were needed for the takeover of Honduras and the assassination of President Roberto Suazo Cordova. The plot was thwarted Thursday, just two weeks before it was to be launched, when the FBI arrested eight people.

Latchinian's delivery of 72 British-made Saladin armored cars was completed in July. The arrival of the armored vehicles, which are equipped with 76-mm cannons, comes on the heels of a similarly unprecedented build-up of Soviet-supplied tanks in neighboring Nicaragua.

The sale was negotiated with former Honduran armed forces commander Gen. Gustavo Alvarez, who was ousted last March in a barracks coup. Alvarez, who now lives in Miami, was not named in the indictment of the alleged coup plotters.

But at least two of those named Thursday by the FBI are known to have close ties to him. They are Latchinian and Honduran Gen. Jose A. Bueso Rosa, 47, the military attache at the Honduran Embassy in Chile. Bueso was assigned there after being relieved of his duties as chief of staff of the military at the time of Alvarez' ouster.

In Tegucigalpa, the Honduran capital, government officials said yesterday that they would seek extradition of both Alverez and Bueso, the Associated Press reported. Attorney General Elizabeth Chiuz Sierra said the group would face charges of high treason and related crimes in Honduras.

In Miami, Alvarez denied that he was part of the plot. "I don't have anything to do with this," AP said he told a local radio station. "If I had known, I would have told the proper person, because the moment I knew about something like this I could be considered an accomplice under the laws of this country."

Honduras has been the staging area for the past three years for U.S.-backed rebels who are trying to overthrow the government of Nicaragua. According to a source close to the Honduran military, the purchase of the 1950s-era Saladin armored cars was made to counter the arrival in Nicaragua in recent years of sophisticated Soviet-made main battle tanks. A Pentagon report this spring said Nicaragua has taken delivery of 44 Soviet T55 tanks.

Asked about the military utility of pitting Saladins against far heavier and more powerfully armed Soviet tanks, several military exports in the United States said the Saladins would be overwhelmed.

"It is a marginal defensive weapon against main battle tanks, and you would have to be crazy to try to launch an offensive attack against Soviet T55s with Saladins," said Phillip Karber, a widely published expert on armor and a vice president for national security programs at BDM Corp., a major U.S. military consulting company.

According to a Honduran source close to the sale, U.S. military officers in Honduras thought the purchase of the lightly armored six-wheeled vehicles was a bad idea. U.S. military assistance to Honduras has increased dramatically in recent years, jumping from $4 million in 1980 to $77.5 million in 1984. In the past year, as many as 5,000 U.S. troops have taken part in military exercises there. The Saladins, however, reportedly were purchased with Honduran military funds and not with U.S. aid.

The Saladin aquisition was initiated last year under Alvarez' tenure as armed forces commander. Previously, the Honduran military had only 17 light tanks and five armored "dune buggies." Alvarez was ousted in part for running the military with an iron hand and tolerating little criticism. He was also blamed for widespread corruption and mismanagement, which he has denied.

The Saladins were obtained through negotiations both with Latchinian's Miami-based arms company, a longtime arms supplier to Honduras, and with a much larger Los Angeles-based arms supplier called Sherwood International Export Corp.

According to a source close to the sale, the Honduran government last year committed itself to pay Latchinian $7 million over five years. Latchinian, according to this source, bought the armored cars from Sherwood International for $5 million.

The Honduran government paid Latchinian $1.2 million on delivery of the armored cars, the source said, and was supposed to pay the arms dealer the remainder over the next five years in coffee contracts worth about $5.8 million. Latchinian's arrest for plotting to overthrough the Honduran government appears to jeopardize payments for the armored cars.

A Miami-based lawyer for Sherwood International said yesterday that the company, through a Cayman Islands-based affiliate called Cromwell Ltd., bought the armored cars last December in Belgium.

The lawyer, E. Richard Alhadeff, said the vehicles were then sold to Latchinian's company, G&J Export Corp., in April. Alhadeff said the armored cars were shipped out of Belgium, after having been inspected there by Honduran military officials.

In Honduras, a source close to the military said that the Army wanted the Saladins for sound military reasons. Among those reasons, the source said, were the range and piercing power of the Saladin's cannon and the vehicle's speed up to 45 miles an hour , which would enable it to move quickly to the Choluteca border area near Nicaragua.