President Reagan, in a rousing sendoff of a lobbying campaign on behalf of U.S. aid to antigovernment guerrillas in Nicaragua, charged yesterday that Sandinista leaders have become, "as they had always planned, eager puppets for the Soviets and the Cubans."

Reagan made the statement at a White House meeting with about 180 Central Americans who flew to Washington from Miami Sunday to lobby Congress on behalf of the Nicaraguan insurgents. The visitors are the first wave of a major influx expected here as the administration seeks to reverse the congressional ban on Central Intelligence Agency funds for the insurgents, or "contras."

The visitors gave an enthusiastic reception -- including prolonged applause and shouts of "We love you" -- to Reagan, who used the occasion to unleash some of his toughest language against Soviet activity in the Western Hemisphere and the Nicaraguan government.

"The Soviets' plan is designed to crush self-determination of free people, to crush democracy in Costa Rica, Honduras, El Salvador, Guatemala and Panama. It's a plan to turn Central America into a Soviet beachhead of aggression that could spread terror and instability north and south, disrupt our vital sea lanes, cripple our ability to carry out our commitments to our European allies and send tens of millions of refugees streaming in a human tidal wave across all our borders," Reagan said.

He termed the Nicaraguan government a "dictatorship" that practices "tyranny," despite "reassuring words of peace to the outside world." Reagan charged that the Sandinista regime is seeking "to crush personal freedoms, attack the church, nearly wipe out an entire culture -- the Miskito Indians -- summarily execute suspected dissidents, drive leading democrats into exile and force young boys to defend the revolution while Soviet-bloc advisers sit in Managua living off the people."

Reagan compared the government-directed relocation of Nicaraguans from a strip near the Honduran border in recent days to "Stalin's tactic of Gulag relocation" and said that it is similar to "forced relocation" in the Ukraine, Vietnam, Cambodia, Afghanistan, Angola, Ethiopia and Cuba.

"The United States was on the side of democracy during the fight against Somoza, and we're on the side of democracy today," he said.

The president called for "all freedom-loving people to unite in demanding an end to the Sandinistas' intimidation." He did not explicitly mention the drive to reverse the congressional ban on CIA financing for the insurgents, but maintained that the dream of a bright future for Central America "can quickly become a nightmare if we don't stand behind the brave men who are putting their lives on the line for the cause of freedom in Nicaragua."

The visiting delegation includes business and political figures from a variety of Central American and South American countries and representatives of exile groups in Miami.