The Reagan administration has tentatively decided to train Nicaraguan contra troops in the United States after Costa Rica, El Salvador and Honduras objected to use of their territory, U.S. officials said yesterday.

The Army, Navy, Air Force and Marine Corps have been directed to make detailed recommendations for suitable training sites in the United States, sources said. They have been told the site must be remote to minimize adverse publicity and citizen opposition.

Although Fort Benning in Columbus, Ga., has been used to train Salvadoran unit leaders and would be ideal in many respects, military sources said this site has too high a public profile. Air Force bases away from population centers are the leading candidates, officials said, although they would not specify which one is at the top of the list.

The administration tried to persuade several Latin American governments to allow use of their territory, officials said, but ran into opposition in Costa Rica, El Savador and Honduras. Governments there did not want to invite retaliation from the Sandinista government of Nicaragua, sources said.

As U.S. military leaders zero in on U.S. training sites, Gen. John R. Galvin, head of the Southern Command in Panama, which commands U.S. forces that move in and out of Latin America, is drafting a detailed military plan for making the best use of the $ 100 million in military and economic aid that Congress recently approved for the contras, as the rebels are known.

On Friday, President Reagan signed the executive order that opened the way for the new flow of money to the 20,000 contras in Nicaragua. Under congressional restrictions, $ 70 million can be used for military hardware, $ 27 million for medical supplies, food and other nonlethal aid and $ 3 million for monitoring human-rights conditions.

The State Department will provide overall policy guidance for the contra program, the U.S. military will train contra unit commanders and the Central Intelligence Agency will support the contra operations at arm's length from outposts around -- but not in -- Nicaragua, according to administration officials.

Planners at the Defense and State departments, the CIA and the White House are moving ahead on the assumption that Congress, now that it has voted to resume U.S. aid, will go along with low-profile training of selected contras on U.S. soil. Salvadoran troop leaders have had small-unit training at Fort Benning, but there has been no known training of contras on U.S. soil.

Besides locating the training site, government agencies are wrestling with the question of how to make the best use of the $ 100 million that proved so hard to get from Congress. Congress cut off U.S. support to the contras two years ago, and private organizations have been trying to fill the gap. But officials said yesterday that there is no long-range military plan for using the $ 100 million and the amounts the administration will try to get later.

Issues being addressed by the Southern Command, the Joint Chiefs of Staff and the White House National Security Council range from war-fighting tactics to programs for winning over the general populace of Nicaragua, officials said. An administration planner deeply involved in the contra effort said one question troubling Pentagon leaders with Vietnam service is: "How are we ever going to cut this thing off?"

President Reagan, Defense Secretary Caspar W. Weinberger and other top administration officials have vowed to keep their anti-Marxist effort in Latin America from ballooning into a Vietnam-style commitment. But once Army Green Berets start training contras in the United States, the administration expects critics to cite parallels to the early days of that conflict.

The plan, officials said, is to train unit commanders, not green soldiers, in the United States. The unit commanders would then return to Nicaragua to pass on their skills to their men. The training will include how to handle the weaponry the contras will be getting, ranging from antiaircraft missiles to light artillery, along with field tactics suitable for guerrilla warfare.

Radio gear to enable small contra forces to keep in touch with each other and call in supply aircraft is one of the big needs, according to U.S. military planners. Buying that gear and training the contra squad and company commanders to use it, officials said, will be expensive and time-consuming.

Galvin, the Joint Chiefs, CIA specialists and White House officials are trying to set objectives for the contras' war, officials said. One central question is whether the antigovernment forces should be trained for a long, small-unit campaign -- as the Vietcong conducted in Vietnam before North Vietnamese troops took over that war -- or organized and equipped for large-unit actions.

Congress broke the $ 100 million into two installments. The first $ 60 million is now available. It will be a mix of military and nonmilitary items, with rifles, ammunition and grenade launchers expected to be in the earliest deliveries. The remaining $ 40 million becomes available Feb. 15 and can be used for heavier weaponry, such as artillery. Congress can halt the February aid by a vote of both chambers.

Reagan is required under the aid legislation to report to Congress periodically on human-rights issues and progress toward regional negotiations to bring peace to Latin America.