It began with Sunday afternoon training in the Everglades, political klatches in Miami condominiums and stealthy raids by former Nicaraguan National Guard officers determined to rid Nicaragua of its new Sandinista rulers.

Three years and more than $80 million later, the anti-Sandinista rebel movement has grown into a serious war pursued by thousands of guerrillas in the mountains of their Central American homeland. Because money and advice from the Central Intelligence Agency was responsible for much of the transformation, the rebellion also has become an important item on the agenda for President Reagan's second term in office.

The Reagan administration currently is wrestling with the question of renewing official U.S. support for the supposedly covert war, which has become increasingly overt in part because the administration has helped publicize some aspects of the operation in an evident effort to intimidate the Sandinistas and their Cuban supporters.

This -- as well as the general conduct of the war -- has produced a sense of unease within the CIA. Moreover, the debate around the agency's role in the conflict intensified this month when members of the House intelligence committee criticized it for exercising "extremely poor management" in running the program against Nicaragua.

That criticism, which centered on the production and distribution of a psychological warfare training manual for the contras, as the rebels are known, was a public echo of a growing chorus of similar criticisms and doubts about the agency's performance by intelligence professionals, U.S. military personnel and Foreign Service officers with firsthand knowledge of the effort to undermine the Marxist-led Nicaraguan government.

Controversy surrounding the management of the covert war has brought a renewed sense of vulnerability within the agency after a period of relative calm in which many there felt the CIA had won a hard-fought battle to regain an apolitical and professional image, according to intelligence professionals.

The debate also has left the contras, the men who do the fighting against the Sandinistas, fearful about being dumped by the United States in the way Cuban exiles, Kurdish mountain warriors and Angolan rebels have all felt they were abandoned during the past two decades when they became politically inconvenient for the United States. The contras and their concerns will be examined in a second article Monday. 'Casey's War'

"If you're going to overthrow anybody you have to do it pretty quickly," said one CIA veteran of Nicaragua's "secret war." "These operations always unravel -- unless they take over the country -- and they always make a mess."

While Congress comes in for some criticism, many intelligence professionals point fingers at Director of Central Intelligence William J. Casey.

"It's really Casey's war," one of them said.

Like other critics who have been involved in the operation, he spoke on the condition that he not be identified. But David Atlee Phillips, a founder of the Association of Former Intelligence Officers and the CIA's Latin America division chief in the early 1970s, said that their general concerns are shared by a large part of the intelligence community.

Phillips said there is no consensus, but "a significant portion of the intelligence community would be just as happy to see secret wars that aren't really secret go away."

"It was the president's judgment that it was in the United States' interest to do it," said one senior intelligence official defending Casey's role in the operation. "Somebody's got to look at the national interest, not just CIA's interest. And when the president and the administration tell you to march, you march, after having had your say."

But much of the criticism of Casey centers on how he used his say. Casey is both CIA director and a personal confidant of President Reagan. He came to his present position after serving as Reagan's campaign manager in 1980.

With such credentials, Casey's critics in the intelligence community contend that he was in a good position to defend his bureaucracy from ill-conceived administration policies.

Instead, Casey is said to have embraced and defended a paramilitary program pursuing the vague, protracted goal of "pressuring" the Sandinistas.

"It was nickel and dime," said one diplomat, speaking of the program as a whole and voicing a complaint that seems almost universal among those people who worked with it. If it was going to be done, "it should have been serious from the beginning. We should have put $100 million into it at the start, not $19 million," the first amount Reagan authorized in late 1981. "We should have pushed hard instead of drawing it out. But it was hubris; we were going to knock off these little brown people on the cheap."

When asked for comment, CIA spokesman George Lauder said the agency was not giving briefings on Central American questions at this time. After a point-by-point review of the criticisms raised in this article, Lauder said that "none of the senior officers of the agency share the views of the anonymous critics. Moreover, last week in the agency's auditorium, Mr. Casey addressed an overflowing audience of employes on such matters and received a standing ovation." The Conflict's Beginnings

Although much has become public about the war against the Sandinistas and the CIA's role in it, important points about its origin still remain obscure. The extent of CIA contacts with Nicaraguan conservatives before the 1979 revolution toppled dictator Anastasio Somoza, for example, has not been outlined on the public record.

But it is clear that the agency was put in touch with a small, ill-funded and poorly organized anti-Sandinista group in mid-1981 through an informal network of conservative U.S. civilians and former CIA employes in Central America. That group was run by exiled members of the Nicaraguan National Guard and agents of the Argentine military government intelligence service. After talks between senior U.S. and Argentine officials in the summer and fall of 1981, U.S. funding of the paramilitary program built on that group began in December, according to sources involved with the operation at the time.

From late 1982 on, Congress proscribed any attempt to overthrow the Nicaraguan government, and funding levels were predicated on the assumption that the paramilitary program was intended only to "interdict" alleged arms shipments from Nicaragua to El Salvador's rebels.

On the other hand, the rebels doing the fighting were uninterested in interdiction and hoped to regain control of their country. When the Nicaraguan population failed to flock to their banner after major offensives in 1982 and 1983, what was left was an army without a country and without the resources to take one.

Casey is criticized for pushing ahead with the mining of Nicaragua's harbors and light bombing attacks on Nicaraguan installations rather than actively pursuing possible negotiations or other means of winding down the operation. The mining had little long-term impact on Nicaragua, but the flouting of international law was a major element in the congressional decision to cut off aid to the Nicaraguan rebels altogether.

Casey meanwhile accepted and passed on to Congress what were almost certainly inflated figures for the troop strength of the anti-Sandinista forces, according to U.S. intelligence sources close to the operation. These sources said that they did not know whether this was intentional or simply an uncritical acceptance of figures supplied by field commanders anxious to build up their own importance and increase their budgets.

The figures, said one intelligence official, were a means to show that the anti-Sandinistas were "doing something."

"We always asked the numbers question," said Sen. David F. Durenberger (R-Minn.), a member of the Senate intelligence committee and considered likely to be its chairman in 1985. The troop counts were supplied to indicate political "popular response" and military "capacity," Durenberger said.

Over time, however, statistics showing anti-Sandinista forces growing from a few hundred in 1981 to more than 10,000 in 1984 were greeted with considerable skepticism by the congressional committees, according to congressmen and staff members.

"No one is wittingly trying to mislead anybody [but] there is a high degree of . . . ambiguity," said one intelligence source.

In the investigation that centered on a controversial psychological warfare training manual for the Nicaraguan rebels, members of the House intelligence committee criticized the program against Nicaragua for "extremely poor management."

"The entire publication and distribution of the manual was marked within the agency by confusion about who had the authority and responsibility for the manual," the committee said in a Dec. 5 press release issued at the conclusion of its investigation of the affair. "The incident . . . illustrates once again to a majority of the committee that the CIA did not have adequate command and control of the entire Nicaraguan covert action."

Rep. Norman Mineta (D-Calif.), a member of the committee, said in an interview that this criticism sprang from Casey's "swashbuckling" way of running the agency.

"The CIA was rebuilding itself as a credible intelligence-gathering, intelligence-analysis group," Mineta said. "But what I see Casey doing is turning it into a paramilitary agency to implement policies, and I do not think that is what the Central Intelligence Agency is all about."

The administrative organization of the paramilitary program was so poor, Mineta said, that when it came to reviewing the controversial manual, "over at Langley [CIA headquarters] we've got 18,000 people working for the agency, and no one read the darn thing."

Mineta has called for Casey's resignation on numerous occasions.

According to intelligence officials, the overall direction of the covert action against Nicaragua was dealt with by interagency working groups including State Department, Pentagon and White House representatives as well as the CIA. But the day-to-day conduct of the paramilitary operation itself, the "secret war," belonged mainly to Casey and his subordinates. Reprimands and Responsibility

The view of Casey from inside the intelligence community centers more on organizational deficiencies and his apparent disinclination to use formal chains of command in an agency that relies on tight organization for secrecy and efficiency. But it is equally controversial.

During the peak of U.S. support for the anti-Sandinista rebels in 1983 and early this year the deputy director of operations at the CIA was John H. Stein. But Stein, now inspector general, was described by officials familiar with the operation as taking little direct role in running the war.

That duty instead fell to Duane R. (Dewey) Clarridge, then Latin America division chief and an enthusiatic partisan of the project. Clarridge had little or no background in Latin America, and he was transferred to the European division earlier this year.

Many members of the intelligence community considered the flap about the rebel training manual an overblown issue exploited in Congress for partisan purposes. But the question of who would bear the brunt of the blame once the issue arose provoked further internal criticisms of Casey.

Phillips said that the agency is used to seeing accountability for success or failure clearly assigned up and down the chain of command. But under the present CIA administration, Phillips said, it seemed that "when things go right they're on top, and when they go wrong they're nowhere around."

According to sources familiar with the Nicaraguan operation, Clarridge received no reprimand despite his intimate involvement with the operation. Instead, his subordinate, the task force director, was reprimanded.

The CIA station chief in Honduras was reprimanded, but his subordinate, who was closer to the rebels, was not. The subordinate was recommended for punishment, but, because previously he had been given an award by Casey, there was no punishment.

Casey personally visited Honduras, the base for most of the anti-Sandinista operations, in 1982 and in June 1983.

Clarridge and other CIA officials accompanied him on the second visit, which came as the Reagan administration was preparing a major escalation of its pressures on Nicaragua through expanded military maneuvers in Honduras and a major naval presence off Central America's coasts. Government officials in Honduras and El Salvador recall this group of men looking like a collection of conventioneers in tropical shirts.

Clarridge followed up with visits in July and October, according to U.S. intelligence officials. But these sources said that while Clarridge pushed the rebels to mount a major offensive, he offered them no effective logistical support to carry it out. With only two old C47 airplanes to back up their efforts and many organizational problems still unresolved, the October 1983 offensive by the rebels was a failure.

According to administration officials, a calculated aspect of the covert action against Nicaragua was the bluff of imminent intervention and the presence of U.S. power backing up the rebels, even though the actual U.S. investment in money and manpower was kept low. Part of the bluff involved making the CIA-funded war a public secret in 1982 and 1983, these sources said.

A May 1983 report from the House intelligence committee discussing committee efforts to curb U.S.-backed rebel efforts during fiscal 1983 said, "Throughout, executive branch officials made little effort to mask U.S. support, going so far . . . as to encourage media discussion."

But Phillips noted that such tactics have had a demoralizing effect in some parts of the agency that have trouble enough maintaining the secrecy vital to their operation without leaks, as he put it, at the bottom, on the left, at the top and on the right.

"The intelligence professional watches the leaks in the ship of state with great dismay," Phillips said.

The Nicaragua operation was "being used as a signal instead of as a means to an end," he continued. "Most of us would be happy if we were back in the business of performing tasks rather than being smoke-making machines."

Next: Who the contras are CAPTION: Picture 1, CIA Director William J. Casey, His critics say he embraced the "secret war." Picture 2, Rep. Norm Mineta: "I do not think that is what the [CIA] is all about." Photos by James K.W. Atherton -- The Washington Post