CAsh payments to Jordan's King Hussein are part of one of the Central Intelligence Agency's most effective and wide-reaching funding and intelligence-gathering operations, according to informed sources in Europe and the Middle East.

Other Arab leaders and businessmen who, like Hussein, have cooperated with the agency in extending American influence in the oil-rich Persian Gulf area during the eclipse of British power there have collected tens of millions of dollars in commercial fees from American defense industry firms.

No evidence has surfaced that the CIA directly channeled lucrative arms deals to its friends; but one American investigator who looked at these large commissions labels some of them as "reaching in" efforts by the agency to get at Arab rulers through well-placed middlemen disposed to help the CIA.

The time, effort and whatever cash the agency has invested in building up a network of close and interlocking relationships with key Arab policymakers appears to have paid off handsomely for CIA objectives.

Hussein is one of the two most important Arab policymakers whose close ties to the CIA have long been considered a more or less open secret in the Arab world, where there has been little public political controversy over their roles.

The other is Kamal Adham, Saudi Arabia's head of national security and liaison man with the CIA.

Adham, brother-in-law of the late King Faisal, has also become one of the Middle East's most important businessmen, garnering commissions for the sale of Boeing and Lockheed aircraft, among other items, through a corporation controlled by his, family and associates.

Like Hussein, Adham is a pivotal figure in Arab politics whose influence and business arrangements reach beyond the borders of his own country. He is extremely close to the Saudi ruling family on the one hand and to Egyptian President Anwar Sadat on the other.

Adham's closest friends in Saudi Arabia describe him as "a friend of America" and as one of the shrewdest political operators in the Middle East.

While Sadat's predecessor, Gamal Abdel Nasser, was trying to overthrow the conservative Saudi regime in the 1960s, Adham carefully cultivated Sadat. An authoritative source who declined to provide any other details said that at one point Adham was providing Sadat, then Egyptian vice president, with a steady private income.

In September 1970, Sadat became president on Nasser's death and eight months later had crushed a Soviet-backed plot to overthrow him. Intelligence sources have suggested that the CIA alerted Sadat to the plot.

Sadat changed the shape of Middle East politics in July 1972 by abruptly expelling the 15,000 Soviet military advisers Nasser had allowed to be posted in Egypt, paving the way for the diplomatic honeymoon Sadat enjoyed with former Secretary of State Henry A. Kissinger after the 1973 Arab-Israeli war.

Saudi Arabia and Jordan have also been essential footholds for expanding American influence in the Persian Gulf, according to many sources in that area.

Hussein used his personal influence to help draw Oman's Sultan Qaboos Bin said closer to the American sphere of influence. An influential go-between in that relationship was a Saudi-born Jordianian businessman named Ghassan Shaker, who has become a major figure in arms and other sales to Oman since then.

Shaker also was involved in bringing a publicity-shy American company, Vinnell Corp. of Los Angeles, in to train the highly sensitive Saudi national guard. Although Shaker has denied any connection with Vinell, which recruited Vietnam veterans for Saudi Arabia, he has been listed in court papers in Los Angeles as part owner of the reorganized corporation.

In addition to that the agency apparently sees as Hussein's "anchoring" role for Arab moderates willing to live in peace with Israel and to combat Palestinian extremists, Jordan also shares in conventional intelligence activity.

Jordanian intelligence officers have moved into jobs in Oman and other key Persian Gulf sheikhdoms that would have obviously rejected Americans for sensitive posts.

Jordan provided material encouragement to Kurdish rebels in Iraq during the 1974-75 civil war, in which the CIA also covertly helped the Kurds, who were forced to surrender when Iran's Shah Mohammed Reza Pahlavi -- another ruler with close CIA ties -- cut off aid to them.

The CIA also appeared to be able to use Jordan as a springboard for counterterror actions against Palestinian groups in Lebanon, and was reportedly in contact through jordan with Lebanese Christian militiamen whom Hussein helped to supply during the Lebanese civil war last year.

The immediate access the senior CIA operatives in Jordan had to the king gave the United States "unparalleled flexibility" in intelligence-gathering, according to one knowledgeable source.

It also led to the speedy withdrawal of one American diplomat who complained to the king that the embassy in Amman did not have that kind of access. After the CIA got wind of the complaint, Washington transferred the complainant.

On the day the 1973 Middle East war erupted, the Amman station chief spent several hours with the king, alternately consoling him because he had not been told by Sadat of the day the war would begin and trying to persuade him that Jordan should stay out of the war.

As aware as the station chief that his forces would cut to ribbons without air cover, Hussein followed the advice.