Langhorne A. (Tony) Motley, chosen by President Reagan to direct U.S. policy in Latin America, yesterday won the Senate Foreign Relations Committee's unanimous recommendation for confirmation as assistant secretary of state for inter-American affairs.

The committee acted after a brief hearing in which Motley, who had been serving as ambassador to Brazil, endorsed Reagan's determination to combat leftist influence in Central America and warned that Americans must "guard against impatience" in dealing with the strife-torn region.

"There, terrorists and opportunists are exploiting local grievances rooted in decades of inequality," he said.

"They seek to impose a 'quick fix' based on imported communist power and ideology. But the truth is that there are no quick fixes."

Motley, 45, was born in Brazil. He was a land developer in Alaska before joining the administration two years ago.

Motley was picked for the assistant secretaryship last month when Reagan dropped the incumbent, Thomas O. Enders, who had become the target of suspicion that he advocated negotiations of a power-sharing nature with the leftist insurgents in El Salvador. Although he refused to discuss specifics, Motley appeared to confirm reports that Reagan's special Central American envoy, Richard Stone, is seeking to arrange a dialogue between representatives of the guerrillas and the Salvadoran government.

The Washington Post reported last week that, while the administration's aim is to induce the Salvadoran left to take part in presidential elections scheduled for late this year, Stone plans to talk to the guerrillas' political representatives and is trying to come up with an agenda sufficiently broad to attract them into negotiations.

"The key element, in my view, is that they talks go on between the guerrillas and the government," Motley testified. "The president's charge to Ambassador Stone is that he try to facilitate that. As to who talks to whom and when and where they talk, there has to be an element of confidentiality in this process."

Motley turned aside questions about covert U.S. aid to guerrillas operating against Nicaragua's leftist government from Honduras, and plans for increased training in Honduras of forces from Central American countries friendly to the United States.

"I am unaware of any private arrangement with Honduras," he said. "I don't see any increase in the American military presence in Honduras. I have no indication to believe there would be an increase in their numbers."