The former CIA station chief in Costa Rica has contradicted a top-ranking agency official who assured the House intelligence committee last October that the CIA was not helping to resupply Nicaraguan rebel forces in 1985 and 1986.

Tomas Castillo, a pseudonym for the station chief whose testimony behind closed doors to the Iran-contra investigating committees last Friday was made public yesterday, described secret CIA support of the resupply airlift to the contras, which included providing information on safe air routes and weather and other intelligence data. The support occurred during periods when CIA participation in the war was prohibited or sharply restricted by Congress.

Along with telegrams and other documents released yesterday, Castillo's testimony described a pattern of CIA involvement in Central America and at headquarters that committee members said yesterday was far deeper than senior CIA officials had led them and the congressional oversight panels to believe.

Specifically, Castillo disputed the description of the CIA's role given by Deputy Director of Operations Claire George nine days after a C123 cargo plane involved in a resupply mission was shot down in Nicaragua. Testifying Oct. 14 before the House Permanent Select Committee on Intelligence, George said the agency was "not involved directly or indirectly in arranging, directing or facilitating resupply missions conducted by private individuals in support of the Nicaraguan Democratic Resistance."

But when Sen. Sam Nunn (D-Ga.) read Castillo this statement at Friday's closed session, Castillo said he would "have to disagree with that," and added: "My participation did facilitate because it provided the information" that permitted the supply drops to rebels inside Nicaragua to take place.

Castillo, testifying under a grant of limited immunity from prosecution, identified two of his immediate superiors as having known about his activities: the chief of the CIA's Central America task force, previously identified as Alan D. Fiers; and the head of the Latin American Division, designated as "L" by the committees.

The former station chief, who has been on administrative leave since early this year, also acknowledged that he had initially misled the CIA's inspector general and the Tower review board about his activities in Costa Rica. But he tried to explain his misstatements by citing "guidelines" he had been given by "L," which he was told had been arranged by George. His explanation was that he had been assured that the investigators would limit their questions to the resupply operation.

But a source close to the Tower board said Castillo was recalled for questioning after the discovery of his secret messages to North and other material. After hours of cross-examination, this source said, Castillo "dramatically" changed his story. Based on this reversal, the CIA inspector general reopened his inquiry, the source said.

Nunn, a member of the Iran investigating panel and the Senate Select Committee on Intelligence, said yesterday, "If what Mr. Castillo testified to {Friday} is accurate . . . a very strong case can be made that the information the CIA has provided Congress from very high levels and particularly provided the intelligence oversight committees . . . was not accurate."

In a news conference, Nunn was joined by Sen. William S. Cohen (R-Maine) in saying that responsibility for fully investigating the possible misleading of Congress by the CIA should be left to the permanent oversight panels. "The Iran panel's plate is already too full," Nunn said.

Castillo, who has been with the agency 20 years, went to Costa Rica as station chief in 1984. After Congress stopped all U.S. assistance to the contras effective that October, Castillo said, he saw his role as bringing together the "ragtag bands" of rebels along the Nicaragua-Costa Rica border.

When Ambassador Lewis A. Tambs arrived in 1985 with directions from White House aide Lt. Col. Oliver L. North Jr. to open a military "southern front," Castillo began expanding his role.

He told the committees it was his idea to build a secret airstrip on a peninsula close to Nicaragua for use by planes supplying the rebels.

An exchange of cables between Castillo and agency headquarters in Langley, Va., in August 1985, made public yesterday, suggests how the upper echelons of the agency wanted to support the contras while keeping their bureaucratic distance from events in the field.

Castillo reported that Tambs had obtained Costa Rican approval for the airstrip to resupply the southern front. In its "eyes only for chief of station" response, CIA headquarters said it was "pleased" with the Costa Rican decision, but added: "This said, we must emphasize to station that neither CIA or {Department of Defense} can become involved either directly or indirectly."

Castillo said he never again reported to Langley on the airstrip, but he observed every step of progress on the site, and discussed it at meetings with other station chiefs.

In the fall of 1985, new and somewhat less restrictive legislation permitted the CIA to establish secure communications with the contra comandantes. At the same time, North and his chief helper in the private sector, retired major general Richard V. Secord, were organizing an airlift based in El Salvador that could supply rebels in both northern and southern Nicaragua.

Castillo's involvement in the contra war deepened, he indicated, when he received a KL43 encryption device that allowed him to securely relay information to the Secord airlift operation on sites for supply drops. In effect, he became the middleman between the contra comandantes in the field and the North-directed airlift.

In April 1986, Castillo told the committees, he requested from headquarters "flight vector information" for an L100 cargo plane dropping "lethal material" to rebel units inside Nicaragua. The information, Castillo said, gave the pilots the best route based on intelligence information on enemy radars, surface-to-air missile positions and "curvature of the earth."

According to testimony and exhibits introduced last Friday, flight vector and weather information was provided on separate flights proposed in April, May and June.

In the first week of hearings, Secord testified that he had asked the late CIA Director William J. Casey for weather and intelligence information and that Casey had said he would "look into it." Secord maintained, however, that he had never been given the information.

According to Castillo, his contacts with North -- which he acknowledged were outside the chain of command -- were known to both his immediate boss, Fiers, and to "L." He also said that he told "L" that he had obtained the KL43 encryption device from North -- an assertion that has been denied by "L" in a deposition, according to one committee member.

In May 1986, during a regional CIA meeting, Castillo raised a concern about his activist role with Fiers and "L." At that session, he said, they agreed to his suggestion that a Nicaraguan be trained to take over the communications role he had been performing.

But in July, headquarters dispatched a cable shelving the idea for what Castillo called "political reasons." However, headquarters did not order Castillo to stop his activities. Instead, it noted that it had repeatedly told Congress that CIA personnel "do not have any relationship with the private benefactors {the Secord operation}."

Nunn, remarking that this was a very "unorthodox" cable, asked Castillo whether it was not true that "they were covering their rear end back in Washington."

"Yes, sir," he said.

"And they were leaving you hanging out there," added Nunn.

An undertone of concern about whether the activities were proper runs through the documents and recollections of Castillo released yesterday. In discussing a plan to have a C7 belonging to the airlift land at the international airport in San Jose, Costa Rica, Castillo recalled saying to Tambs: "We really shouldn't be involved in this."

At one point, Castillo sent North a proposal to create a 2,500-man strike force that could move northwest into Nicaragua. But when asked about this by committee members he said he was "just brainstorming."

In a related development, Eugene Hasenfus, a crewman who survived the Oct. 5 shootdown of the C123 cargo plane in Nicaragua, said on ABC's "Good Morning America" that he knew of no CIA involvement in the airlift operation.

Iran-contra hearings resume today with testimony from Assistant Secretary of State Elliott Abrams.