Washington — A leader of the CIA-supported Nicaraguan guerrilla forces asserts that his men are ''winning the war in Nicaragua, but losing it in Washington.'' Adolfo Calero Porto Carrero, political director of the Nicaraguan Democratic Force (FDN), says that the aim of his group is to force the Sandinista revolutionaries to return to their original promise to establish a democracy in Nicaragua. But Mr. Calero says this aim may not be achieved until the Sandinista regime is near the point of collapse.
''When do Marxist-Leninists finally negotiate?'' asked the tall, articulate Calero. ''They only negotiate when they're up to their ears in trouble.''
President Reagan said in an interview on May 4 that the American-backed guerrillas fighting inside Nicaragua were ''freedom fighters'' whose only aim was to get the government of Nicaragua to keep its promises. In an earlier statement, the President had indicated that the sole aim of the guerrillas was to interdict arms being sent by Nicaragua to the anti-government insurgents in El Salvador.
Adolfo Calero said that the guerrillas had blown up a number of Sandinista trucks carrying arms and ammunition, but that their main emphasis was on putting pressure on the Sandinistas.
But the Democratic members of the intelligence oversight committee of the US House of Representatives disagree with the logic of Reagan and Calero. They voted on May 3 to ban any secret aid for military operations inside Nicaragua. The Republican-dominated Senate intelligence committee then voted to approve continuation of current covert funding for Nicaraguan operations, but only through the end of this fiscal year on Sept. 30. The Senate committee members voted to ban funding for such operations after that date unless President Reagan produced a ''redefined'' plan for Central America, which they had approved.
The Democratic members of the House committee argued that CIA aid to the guerrillas was illegal because it violated restrictions against aid that might be aimed at overthrowing the government of Nicaragua. They also contended that the so-called secret war could destabilize Honduras, strengthen Marxist-Leninist elements in the Sandinista regime, increase the chances of war between Nicaragua and Honduras, and alienate key Latin American allies.
In an interview, Calero disagreed with all these arguments.
''If the Sandinista government can't even deal with our forces, they're not going to invite added trouble by fighting in Honduras,'' said Calero.
The white-haired FDN leader said he was not concerned about a possible move by the Senate intelligence committee to ban covert aid to his guerrillas after Sept 30. He predicted that if the guerrillas scored further successes, it would create a ''bandwagon'' effect both here and in Latin America, with congressmen and Latin American allies of the US moving to support the anti-Sandinista movement.
''One thing I will guarantee: If the Latin Americans see the United States taking a firm position, they will support the US,'' said Calero.
But the FDN leader said that actions taken by the US Congress to restrict aid to his forces would have a damaging effect on his men's morale and would encourage the Sandinistas.
Calero said that despite commmon belief in this country, his forces did not consist mostly of former national guardsmen loyal to the late Nicaraguan president Anastasio Somoza Debayle.
The American-educated Calero, who once ran a Coca-Cola bottling plant in Managua, said that he had himself opposed Somoza and had been jailed by him.
Calero said the Nicaraguan guerrilla forces have now grown to a total of 6, 200 men. In addition, he said, some 2,200 Miskito Indians were fighting against the Sandinistas in the eastern part of the country.