Alan D. Fiers, the CIA agent who coordinated the secret supply network to the Nicaraguan contra rebels in 1984-86 on orders from then-Director William J. Casey, has resigned rather than accept another post, informed sources said yesterday.

Fiers, who was chief of the Central American Task Force when U.S. military aid to the rebels fighting the government of Nicaragua was banned, was given a "serious reprimand" by CIA Director William H. Webster in December for remaining silent when superiors misled a congressional committee about the extent of U.S. assistance.

Webster's handling of the Fiers matter was criticized indirectly Thursday by Assistant Secretary of State Elliott Abrams, who had worked closely with Fiers.

Abrams, assistant secretary of state for inter-American affairs, told The New York Times that Fiers "made a great contribution to our interests in Central America and it is an injustice that he is not being rewarded for it."

CIA spokesman Bill Baker, who met with Webster yesterday, called Abrams' comments "inappropriate."

The Associated Press quoted Baker as saying the agency will complain directly to Abrams. "We're very angry at Elliott Abrams," he said. "It's none of his business to be making comments about case officers and their futures."

Webster has disciplined seven agency employees involved in the Iran-contra affair, including Fiers. Two officials, including the former CIA station chief in Costa Rica and the CIA base chief in Honduras, have been fired. Clair E. George, deputy director for operations, and Fiers' boss during the 1984-86 period, resigned at the end of 1987.

Fiers, who sources said had once been in line for a high CIA post, was reportedly offered an assignment abroad.

Sources said yesterday that Webster wants to send a signal to the agency that illegal activities will not be tolerated during his tenure. However, Abrams charged Thursday that the signal sent was: "Don't get involved in controversial programs because you will end up being punished for it."

Testifying before the House-Senate Iran-contra investigating committees last year, Fiers said he had been caught in "a giant nutcracker" between Congress and the executive branch. "I was in the center in a very exposed position," he testified.

Fiers said that as Congress revised what the CIA could and could not do on behalf of the contras, he tried to comply with the law.

"My task force lawyer was whispering in my ear like Jiminy Cricket," Fiers said.

Nevertheless, he said, he got "rambunctious" during at least one period and "let out the reins" limiting his and the CIA's involvement with the private contra resupply network.

That network was operated by retired Air Force major general Richard V. Secord and directed by former National Security Council aide Oliver L. North.