"INSULT THE AMBASSADOR" is the latest weapon in President Reagan's foreign policy arsenal. When Nicaragua's new envoy arrived in Washington last week, he was greeted not with the usual diplomatic niceties but with a note scolding his government for "inviting alien influences and philosophies into the hemisphere. "Tragically, the hostile attitude adopted by Reagan and his advisors toward the Nicaraguan Sandinistas could easily push a country open to friendly relations with the United States into the Soviet camp.

At the heart of the matter lies the Administration's contention denied by Nicaragua--that the leftist government there is Moscow's puppet and supplies arms to guerrillas fighting the U.S. backed Duarte regime in El. Salvador Reagan is also concerned by the substantial Nicaraguan arms buildup and with reported human rights violations against the rightist opposition and the Miskito Indians. Yet Washington has failed to substantiate its accusations. Nor has the State Department made any attempt to view the world through Nicaraguan eyes. Seen from Managua, the present danger is hardly the same one perceived by our foreign policy leaders.

When the Sandinistas overthrew Anastasio Samoza in 1979, the U.S. deserved no credit. President Jimmy Carter long supported the hated dictator, pressuring him to step down only when it became clear a Marxist victory was likely. Still, the new Nicaraguan government was eager to maintain good relations with the United States. But Washington responded by denying Nicaragua all trade and aid, a move that forced the Sandinistas to look elsewhere for help. Moscow was only too happy to oblige.

There is no proof Nicaragua supplies arms to the Salvadoran revolutionaries. While Managua clearly sympathizes with the guerillas. It has reportedly sponsored joint patrols with the Honduras to counter any weapons smuggling.

The recent Nicaraguan military buildup should surprise only the naive. By not discouraging the training of counter revolutionaries on American soil, the Administration has done little to assuage Nicaraguan fears of a U.S. sponsored invasion. Events like the Bay of Pigs remain fresh enough in South American minds to arouse what we must hope is unjustified paranoia. Until the U.S. ceases its open hostility the Nicaraguans will likely continue to buy arms--taking needed resources away from other parts of a troubled economy and fueling what has become a diplomatic vicious circle.

Human rights violations in Nicaragua are difficult to confirm. Certainly the Sandinistas have demonstrated authoritarian impulses through several incidents of censorship and the persecution of opposition leaders. Yet three leading members of the right were recently released from prison, among other positive steps taken since the overthrow of Samoza.

The Administration, it seems, is so committed to its simplistic ideology that it is ignoring American foreign policy interests. By constantly rebuffing Nicaragua's friendly overtures, the United States is denying itself added peace in turbulent Latin America. In the past, the United States has shown it can get along with nations that do not share its political or economic beliefs. The Sandinistas should be no exception. The time has come to turn from, bellicosity to benevolence in Nicaragua.