The Libyan official who arranged two controversial payments totaling $200,000 to Billy Carter said here today that Carter need only ask for the balance of what Libya says is a $500,000 loan.

Ahmed Shahati, head of the Libyan Foreign Liaison Bureau, said the money given Carter comprised, as the president's brother has testified, only the first installments of a half-million-dollar loan he had negotiated with the Arab Libyan Bank.

"If he wants the rest he can have it," Shahati said in an interview here. "It all depends on his wishes."

Shahati, who heads the office that has all but eclipsed the official Secretariat of Foreign Affairs, was the Libyan who first befriended Billy Carter, invited him to Libya and eventually arranged for the loan that has caused such a scandal in Washington. In the interview, Shahati did not go into further detail about Libya's connection with Carter.

The importance of Shahati, who previously was little known abroad, is still little understood. In a government where the lines of responsibility have been systematically blurred by Col. Muammar Qaddafi's efforts to dismantle state bureaucracies in favor of people's committees responsible to the nation's masses, Shahati cannot be under rated.

In the two years, since Qaddafi officially renounced his "executive and administrative responsibilities' to devote himself to "revolutionary action," Shahati has emerged as the head of a parallel Libyan foreign service representing the revolutionary people's bureaus that gradually have been replacing established Libyan embassies abroad.

As the number of people's bureaus has grown, so has Shahati's influence. With 20 former embassies, mostly in Europe and America, already under his control and the 19 Libyan embassies in the Arab world about to be turned into "fraternity bureaus" under the Foreign Liason Bureau, Shahati's influence clearly has surpassed that of Ali Abdel Salam Treiki, who has held the official foreign affairs portfolio since the last government was formed in March 1979.

Foreign diplomats from countries where people's bureaus have been established conduct their business with Libya here through Shahati and his liaison bureau. Those from countries that still have traditional embassies in their capitals do business with Foreign Secretary Treiki.

Since it is Qaddafi's avowed aim to have all embassies converted to people's bureaus under revolutionary committees of students and young radical diplomats, it would seem only a matter of time before Treiki's foreign service disppears.

Whereas Treiki represented formal embassies and traditional diplomacy, Shahati said he represented the people's bureaus, which were the products of Qaddafi's "new philosophy" that his missions abroad be more active and revoluntary and "in tune with Libya's popular democracy."

Libya's diplomatic mission in Washington is one of the people's bureaus in Shahati's network and six Libyans were expelled in April and May for what the State Department said was their role in a campaign of intimidation against exiled Libyan dissidents. European nations particularly Britain and Italy, also had difficulty with the new-style Libyan "diplomacy" and investigators in those countries said they suspected a tie between the people's bureaus and the slaying of several anti-Qaddifi exiles.

Shahati remains an enigmatic figure. A black from the Libyan south, he was a minor diplomat in Libya's embassy in Baghdad, Iraq, in 1969 when Qaddafi and his fellow officers overthrew the reign of the late king Idris. As the story is told in Tripoli, Shahati immediately fired off an enthusiastic cable of support to Qaddafi, thus bringing him to the colonel's eye.

In 1972, when Qaddafi set up his own political party -- the Libyan Arab Socialist Union -- along the lines of neighboring Egypt's own party as part of the infrastructure to facilitate Libya's eventual merger with Egypt, Shahati emerged as the party's secretary general.

After the union with Egypt collapsed, the party faded into oblivion and in 1977 it was officially disbanded.

A socialist who sympathized with the liberation movements then sweeping through the Third World, Shahati was next named head of the newly created Foreign Liaison Bureau, whose initial primary task was to give political and material support to Third World movements.

His bureau soon also took over people-to-people relations with other nations, including the United States, but it was only in 1979, after Qaddafi ordered his revolutionaries to reorganize his embassies, that Shahati's influence spread to the whole gamut of Libyan foreign policy.

As what one Western Ambassador in Tripoli calls" the new wave" spokesman for Libyan foreign policy, Shahati's fervent Third World socialism has dovetailed smoothly with Qaddafi's own messianic view of the world.

Still smarting from their experiences as a Turkish and later Italian colony, humiliated by foreign and economic domination in the post colonial -- they say imperialist -- era, Qaddafi and Shahati's main foreign policy aim remains an insistence on "total liberatin" from all foreign influences. They want freedom from the West, which they see as their most immediate antagonist, as well as from the East, which they fear as a future tormentor -- despite Libya's reliance on Soviet Bloc military purchases.

The existence of Israel is seen as the most humiliating symbol of the divided Arab impotence and dominance by foreign forces. The Libyans see the Israelis as support by the West on what was Arab land until the end of World War II.

It is in this context that Qadafi's singular, if idealistic and perhaps unrealizable, drive for Arab unity must be understood. Libya's effort to forge Unity with Syria this week is considered by Shahati and Qaddafi as the first building stone on which Libya hopes to erect a united Arab nation.

"Unity with Syria is already a fact that we consider an important victory," Shahati said, dismissing all questions about the details that might make the proclaimed union a reality. "What we want now is for the whole Arab world to unite into one nation, just as your own colonial states united after your revolution from Britain. If we can unite 170 million people, with our common resources, we too could be a big power that could no longer be exploited or humiliated."

Despite Shahati's view of the U.S. government as the major villain in the Third World, he remains warm and admiring of the American people and the political ideals and values that underlie American society. It is because of this admiration and respect, he insists, that the Libyan government has sought to establish good relations with Americans through the sort of direct contacts with Americans that first brought Billy Carter to Libya.Carter was, Shahati said, only one of hundreds of Americans who came here and whose relations with Libya were always "proper, legal and correct."

Shahati said he is fond of remembering his three trips to the United States, including his visit to Georgia last year, where he was hosted by Billy Carter.

He even enjoyed his last trip in February, when he visited 10 different states. The winter was particularly fierce for a man of the desert and he recalls when his flight to Wyoming had to be diverted to Denver because of heavy snows.

Driving up to Wyoming Shahati's car suddenly ran out of gas. "Can you imagine," Shahati laughs, "a heart of the United States."