Three weeks after the House vote that gave President Reagan nearly all he wanted to fight Nicaragua's leftist Sandinista government, the relevant intelligence, military and diplomatic experts in official Washington are moving toward a kind of war footing.

It is clear that the aid package for antigovernment rebels, known as contras or counterrevolutionaries, will involve far more money than the $100 million voted by the House, far more people than the 20,000 fighters who will receive it, and far more monitoring and evaluation than either critics or supporters of the program like to acknowledge, according to administration and congressional officials.

Although surrogate troops and not U.S. Marines will spearhead the effort to make the Sandinistas "cry uncle," as Reagan once put it, the contras will be advised and informed, trained and equipped, criticized and evaluated by U.S. intelligence, military and political strategists.

A flurry of interagency meetings and task force planning sessions has begun to give shape to the new program. As expected, it will be run by the Central Intelligence Agency. Army Col. William C. Comee Jr., who has just finished a year commanding U.S.-Honduran military exercises in Honduras, reportedly has been selected to become program coordinator, pending its Senate approval. Intelligence officials and congressional staff members are drafting financial accounting procedures in an effort to avoid the kind of controversy that has plagued previous contra aid programs.

The one-year goals and benchmarks by which the administration plans to judge progress will be critical to future debates over continued aid and over U.S. policy in Central America. The fruits of the new operation will also be an important factor in debate over the wisdom of the so-called Reagan doctrine that calls for support to rebellions against communist regimes around the globe.

If the new surge of aid to the contras is working, administration officials contend, these symptoms will be evident: escalated military activity throughout Nicaragua, possibly including attacks on the capital city of Managua; disciplined combat by the contras, with relatively few civilian casualties or human-rights complaints; rapid growth of the contra forces and a reinvigorated internal opposition, leading to "cracks" in the Sandinista leadership; and Soviet restraint in bolstering the Sandinistas.

If the military ambitions have been clearly delineated, the administration's political aspirations for the contras are more ambiguous. Reagan has never precisely stated what he means by "cry uncle," His chief of staff, Donald T. Regan, told television interviewers in April: "We have to get rid of it the Sandanista regime in some way or another. And what we want to do is to try to help those who are trying to overthrow that communist government, try to force it to have free elections. . . . " But other administration officials have articulated more modest ambitions.

One administration official said an expansion of civil rights in Nicaragua would signify U.S. success; but one of his deputies said that a totalitarian crackdown would mean the administration had succeeded in severely shaking the Sandinista regime.

Secretary of State George P. Shultz called the June 25 House vote "part of a long-term shift of view that's been taking place" nationwide. "We're seeing a growing breadth of support for the basic administration policy in Central America," he said.

But Reagan backers in Congress say the support depends very much on what happens next.

"The contras are on a very thin string with the U.S. Congress," said Mark Falcoff, a conservative Latin America scholar who recently joined the Senate Foreign Relations Committee staff. "They are surrounded by people just waiting for them to fail so they can jump right on top of them, and they know it."

Lawrence Pezzulo, ambassador to Nicaragua under President Jimmy Carter, spoke for many critics of Reagan's policy. "Nicaragua is in bad economic shape already, and this program will bring them to subsistence living, but they won't give in, at least not before the end of the Reagan administration," he said. "The use of U.S. troops will eventually be the only option left . . . . If you're a Democratic presidential hopeful, what else will you be talking about in the summer of 1987?"

To underscore that point, the aid package is expected to get heavy fire in coming weeks from Senate opponents, including some presidential aspirants, in the various committees that have jurisdiction over it. It may also be subject to a liberal filibuster when it reaches the Senate floor next month. But all sides say the House package will pass the Republican-dominated Senate virtually unchanged, if only because no one wants to go through another bruising House debate, which new amendments would trigger.

The package includes $27 million for food, medicine, clothing and other nonlethal aid, $3 million for the contras' human-rights office and $70 million for military training and hardware.

Reagan has decided to return management of the program to the Central Intelligence Agency, with assistance from the Defense and State departments, according to State Department officials. They said aid will be channeled primarily through Honduras and Costa Rica, as it was in the past, with the covert cooperation of those two governments.

Reagan has pledged to spend only the $100 million and to stay away from the CIA's contingency funds, which are considered all but unlimited. Another $300 million in economic aid will be distributed by the Agency for International Development among El Salvador, Guatemala, Costa Rica and Honduras.

A Senate Republican source said the $100 million figure "reflected an assessment of what the political traffic would bear, not an assessment of what the requirements are." All sides assume a larger aid request will be made next spring.

In an effort to avoid a repeat of congressional charges that the CIA overspent previous aid limits through creative bookkeeping when it ran the program before 1984, an intelligence agency task force has been meeting with congressional committee staff members for several weeks to agree on accounting methods, according to a House Democratic source.

The CIA, for example, has not in the past counted its agents' salary costs against aid allocations and did not count the expenses of the "mother ship" its Latin operatives used as a launch platform from which to mine Nicaraguan harbors in 1984, members of Congress complained at the time.

The source said intelligence-related reconnaissance flights over Nicaragua and Honduras, broadcast monitoring and decoding activity, all of which collect data routinely passed to the contras under existing law, have not been and probably will not be charged to the aid program. He was unable to estimate spending for those activities but said $400 million a year "is probably a low figure."

The task force will submit accounting guidelines for approval by the congressional intelligence committees that will monitor the overall program, another source close to the effort said.

"You can bet there's a major drive to avoid the kind of flap we had over the $27 million," he added, referring to House committee charges -- denied by the administration -- that much of last year's nonlethal aid package had gone illegally to offshore bank accounts, obscure corporations and the Honduran armed forces.

House Intelligence Committee Chairman Lee H. Hamilton (D-Ind.) said he was worried about the committees' ability to monitor the new program. "We just don't have the staff for it, and I'm not sure the Central Intelligence Agency does either," he said.

Fred C. Ikle, undersecretary of defense for policy and a central decision-maker on Nicaragua-related matters, said in an interview that U.S. military spending against Nicaragua will be handled largely by the CIA and will go well beyond the $70 million voted by the House.

That, he said, will buy training, primarily in guerrilla tactics, and military hardware ranging from surface-to-air missiles to bullets.

Intelligence work is expensive and outside that tally, but it "has to be directed at trouble spots, and Nicaragua is a trouble spot," he said. "But it is done for broader purposes" than just to help the contras.

In addition, "we are strengthening SOUTHCOM because that is a turbulent region, again because of Nicaragua," Ikle added, referring to the U.S. Southern Command headquartered in Panama.

Congressional watchdogs also expect the virtually nonstop military exercises in neighboring Honduras to be expanded while the new aid program is in effect, though they are not part of it. This is in part because Comee, named by military and State Department sources as the new overall coordinator, is a Vietnam veteran who commanded the Joint Task Force Bravo exercises during the past year.

Fluent in Spanish, Comee was instrumental in setting up the series of exercises that began in 1983 when he was stationed at the U.S. Southern Command headquarters. The maneuvers have involved roughly 24,000 U.S. troops in 12 series of exercises since early 1983, according to Defense Department figures.

The first shipments of new military equipment, which can begin Sept. 1 pending the Senate vote, will probably include antiaircraft weaponry that will allow the contras to defend positions inside Nicaragua, the sources said.

The first sign things are going as planned, therefore, will be increased military attacks on Sandinista positions by contra forces "all over Nicaragua," a State Department official said.

Ikle predicted that the Soviet Union, which has supplied Nicaragua with an estimated $750 million in military equipment since 1979, "will be much more cautious" in helping the Sandinistas now, "realizing from the American commitment that it is a losing game."

State Department officials said they think Soviet aid is not likely to increase in sophistication or quantity much beyond current levels, in which the peak is the Hind Mi-24 helicopter gunship that has routinely decimated contra forces. Recent shipments brought in an estimated 15 new Mi-17 transport helicopters, bringing the Sandinista helicopter fleet to about 40, Pentagon officials said.

The contras will not come close to matching those under the new aid program, but defensive weapons "will make it a more equal battle," one official said.

Ikle and other officials said no comprehensive battle plan or training program had yet been drawn up. William G. Walker, deputy assistant secretary of state for Central America, said one reason for that was old-fashioned superstition about the vote in Congress: Some refused to make plans "because they didn't want to jinx the deal."

SOUTHCOM commander Gen. John R. Galvin told a closed session of the House Appropriations subcommittee on military construction last March 12, long after Reagan proposed the $100 million aid program, that he did not know how or where training might be conducted.

"None of this has been looked at. I haven't been told that we would do training, and nobody has asked me to go find out where," he said.

However, top training priority will be instruction in guerrilla warfare techniques, probably at the contras' clandestine camps in Honduras, including psychological operations aimed at winning over the Nicaraguan population, other sources close to the military effort said.

Some promising contras will be brought to officer training schools in the United States or Panama, the sources said.

If everything goes as well as the administration hopes, one year from now the contras "will be carrying out well-disciplined, coherent operations demonstrating . . . the effective destruction of targets without too much collateral damage," Ikle said.

The United Nicaraguan Opposition (UNO) leaders would like to capture and hold territory within Nicaragua, and that "would make a lot of difference politically if it can be done," but no one is pushing for it, Ikle said.

More important will be "the dynamic of the contra force, whether it is growing or losing people, whether they are knocking at the door to get in or quitting," Ikle continued. At 20,000 armed fighters, the contras are already four times larger than the Sandinista force that overthrew dictator Anastasio Somoza in 1979, but their leaders have said they would like to be 30,000 strong by next July.

"Within a year, we will be seeing cracks in the Sandinista structure," said Alfonso Robelo, one of the three top UNO leaders, at a recent news conference. He said that meant defections of troops or perhaps whole units, increased economic disorder, and a more openly hostile population.

Administration officials and their critics agree that the reaction of rank and file Nicaraguans to the renewed contra effort will be key to the future. Walker said the new aid would be "a great boost to the democratic resistance" within Nicaragua, which could produce internal disruption that would give heart to the contras and show the world all was not well under the Sandinistas.

Elliott Abrams, assistant secretary of state for inter-American affairs, has said progress toward U.S. political goals in Nicaragua would be easy to monitor: "You can see if the press is free, if people can speak out or hold rallies, or if the church is being harassed," he said.

Walker said the opposite situation might also be progress. "If the Sandinistas have to turn the screws down to silence the opposition, that will be an indication that things are going well" for the contras, he said.

More people will try to dodge the Sandinista draft or leave the country as refugees, and "if our policy is right, unity among the opposition should increase," Walker said.

In a year's time, the Sandinistas "should be able to see the outline of the opposition forces they face, and they will act accordingly," he continued.

"Eventually, if it is revealed to them that they are very unpopular, that there is no possibility of a military solution eradicating the contras and that their Soviet patrons would think twice or four times before coming to their assistance . . . then they just might think, 'Hey, maybe we do have to negotiate our way out of this.' "

Ikle predicted a simpler outcome. "Perhaps they won't change colors and become social democrats," he said, "but they might choose to change jobs.