A top envoy of Libyan leader Col. Muammar Qaddafi said yesterday that his country is the victim of an unjustified anti-Libya campaign waged by the Reagan administration and urged that U.S.-Libyan exchanges be resumed.

Ahmed Shahati, former head of the Foreign Bureau in Tripoli and a prominent foreign affairs adviser to Qaddafi, spoke after a week of meetings with State Department officials in which he sought to end a diplomatic freeze imposed on May 6, when the United States ordered the Libyan mission here closed the expelled its staff.

His remarks, at an Arab League luncheon in his honor, left the strong impression that Libya's leadership views the expulsion seriously and is eager to restore diplomatic relations -- which have not be formally cut -- to their former status.

Underlining this, Shahati said that after his contacts with the State Department "the way is open for dialogue." But it was clear from his remarks and those of U.S. officials that, for the time being, whatever dialogue takes place will do so outside normal diplomatic channels.

Shahati complained that in being refused permission to have a mission here, Libya is being singled out for isolation by Washington.

"There are more difficulties between the United States and the Soviet Union, or communist or socialist countries," he said. "Why did they choose only the Libyan office in the United States?"

In ordering the Libyan "People's Bureau" closed, the Reagan administration cited Libya's intervention in Chad, what it called Libyan support for international terrorism and other "provocation and misconduct." Officials said privatey that the United States suspects official Libyan involvement in actions against Libyan dissidents in this country, including the shooting of a Libyan student in Colorado last October.

The United States still refuses to reopen its embassy in Tripoli or allow Libyan diplomats to return here, according to U.S. officials involved in the talks with Shahati. Instead, the United States has proposed that diplomatic relations be conducted through third-county embassies in Tripoli and Washington, the traditional way of doing business between estranged countries. Libya has refused this, however, insisting on reopening the U.S. Embassy in Tripoli along with the People's Bureau here.

Shahati emphasized that Tripoli is concerned about the approximately 4,000 Libyan students here. They and their families bring the numbers of Libyan citizens resident in the United States to about 12,000, he said, and Libyan diplomats should be here to care for their interests.

In addition, Shahati pointed out, about 2,000 Americans live in Libya, most of them working in the oil business. Libya sends about 640,000 barrels a day to the United States.