Lebanon's highest Shiite Moslem religious authority, Sheik Mohammed Hussein Fadlallah, said in an interview today that he has made efforts to release seven Americans and four Frenchmen being held captive here but that his efforts have been fruitless. He expressed fears that their fate may be beyond his control.

Fadlallah, 50, the senior religious figure to Lebanon's 1 million Shiites after Iran's Ayatollah Ruhollah Khomeini, is also believed by some analysts to be the spiritual guide of Hezbollah (Party of God), an extremist Shiite faction that held several of the Americans taken hostage in the hijacking in June of the Trans World Airlines plane.

Fadlallah denies he holds this position or has links to any faction, although he acknowledges that he has special influence as a clerical leader. He also denies any link to the hijackers.

In a separate interview, Ghassan Seblani, a high-ranking official of the Shiite Moslem Amal movement, which undertook negotiations on behalf of extremist Shiite activists who hijacked the TWA plane, said Syria has been embarrassed by delays in freeing of Lebanese prisoners held by Israel in exchange for the June 30 release of the American crew and passengers.

Seblani, a member of Amal's politburo and a U.S.-educated economist, said that what he called the piecemeal approach in letting the prisoners go and repeated denials by the United States that any promise has been made for their release have upset Syria and Amal chief Nabih Berri.

Israel has freed 400 of a total of 735 Lebanese and Palestinian prisoners whose release was demanded by the hijackers. Fadlallah, who said the delay was "not surprising," said that what he called America's failure to deliver on its own promises did not alter his earlier condemnation of kidnapings of foreigners and hijackings.

Fadlallah made a written appeal for the release of French journalist Jean-Paul Kaufmann and researcher Michel Seurat last month, praising them as Orientalists and men of letters.

"I have interfered with all my strength to obtain the release of the American journalist [Associated Press correspondent Terry Anderson] and Kaufmann, who is Jewish, but I have not come to any positive result," Fadlallah said, speaking at his home in Bir Abed, where he escaped a car bomb assassination attempt last March 8.

"My attempts to free the hostages are continuing on more than one level, but I feel I do not have the capabilities to arrive at positive conclusions," he said. "The matter is much deeper than people imagine."

Asked what the obstacles were, Fadlallah suggested that the fate of the kidnaped westerners was linked to intelligence activities and in the hands of countries he would not name.

"The problem of kidnapings in Lebanon is part of a war of intelligence services on the one hand and it is also tantamount to messages and signals between this and that state seeking to pressure certain sides," he said.

This appeared to be an indirect reference to Syria, the major player in the Lebanese arena. Fadlallah agreed that Syria could have a major role in getting the kidnap victims released, but he warned that the "process will not be easy."

Seblani said that there appeared to be no inclination to move toward the release of the seven Americans, kidnaped in Beirut over the last 17 months, "if there is not a sort of payment." He said Washington should at least take a stand on Israel's continued detention of 335 Lebanese prisoners and help in their return home. The United States has said that Israel's transfer of the prisoners, captured in Lebanon, from that country into Israel was a violation of international law.

"We are not planning to push the United States into a corner by saying publicly there is a connection between the hijacking affair and Atlit," the Israeli prison where the captives are being held, Seblani said. He used a Lebanese proverb to illustrate his point: "We don't want to kill the watchman at the vineyards, we just want to eat the grapes."

He complained that Israeli patrols are arresting more Lebanese residents weekly in southern Lebanon and urged that the United States "take a stand and do something."

"Any humanitarian action can only help in accelerating the release of the seven Americans," Seblani said.

The Amal movement and Berri, its leader, reportedly received oral guarantees from Syria last month that Israel would respond to the release of 39 American hostages from the hijacked TWA aircraft by freeing 735 prisoners from Atlit. The United States and Israel have repeatedly denied that any such deal was made for the release of the TWA hostages.

"The promise we got was through the Syrians," Seblani said. Now "they look like they have pulled our leg or that they have had their leg pulled. The promise was that all will be released. Although it was not written or taped, it was a deal between two presidents."

He said he had seen letters exchanged between President Reagan and Syrian President Hafez Assad on the TWA crisis.

"I have seen the letters Reagan sent to President Assad inviting him to intervene in the crisis and Assad's response to Reagan," he said. "The promise was not just the outcome of a telephone conversation. The Syrians are upset and I don't believe they will go for another deal when the first one has not been completed."

Seblani said all the missing hostages are being held by one group, but he did not name it.

Islamic Jihad, a shadowy organization believed to be a front for extremist Shiite groups bent on driving foreigners, especially Americans, out of Lebanon, has said it abducted the seven Americans, two French diplomats and two French journalists.

The same group has claimed responsibility for the suicide bombings against the American Embassy and U.S. Marine and French military headquarters here and bombs in Kuwait in 1983.

Seblani said the group holding the seven Americans was under the influence of Syria because all of Lebanon was under the influence of Syria.

"The Syrians can play a very big role, but they cannot do it by force," he said, referring to possible Syrian attempts to free the captives. "Nothing can be done by force because it will get the hostages killed and fuel hatred toward the Americans, Syria, and us."

Seblani insisted that the guarantees communicated to Syria and, in turn, to Amal "could not have been a trick."

But Fadlallah charged that "as long as the promises made were secret, it is natural for America not to fulfill them."

Meanwhile, in an interview with Reuter, Hussein Mussavi, leader of the hard-line Islamic Amal, accused Reagan of lying after the TWA hostages were freed.

Mussavi, whose faction broke away from Berri's Amal in 1982 but is closely linked with Hezbollah and radical Shiite factions based in Baalbek in Syrian-controlled Lebanon, said Reagan had promised there would be no reprisals and then tried to mount a boycott of Beirut airport.

U.S. and Israeli statements that the release of the TWA hostages and the prisoners in Atlit were never linked were "just pure lying," he said.

Mussavi claimed that the Syrians assured the negotiators in the TWA affair that the Lebanese held by Israel would be freed five days after the Americans were allowed to fly home. Berri, one of the key negotiators, and his aides say the deadline given was one week after the release of the passengers and crew.

Mussavi, one of the most radical of Shiite leaders, said he sympathized with the kidnapers of the seven Americans in Lebanon but that he had no part in their abduction.