Syrian diplomatic efforts to help free 40 American hostages appear to be intensifying after visits here this week by the speaker of Iran's parliament and a leader of a more radical Shiite group and reports today from Beirut that Nabih Berri, the leader of the Shiite Amal militia who is negotiating for the more radical kidnapers, may also soon come to this Syrian capital.

In addition, Syrian President Hafez Assad has just returned from meetings in Moscow with Soviet leader Mikhail Gorbachev. In Washington, State Department spokesmen said today that the Reagan administration has been in touch with Assad, that the Syrian leader has expressed a wish to be helpful, but that "we will quite simply have to see what results."

In this city, where little appears on the surface and often less is said officially, analysts and diplomats cautioned that if Assad is indeed exerting his influence to help free the hostages, the results so far have appeared meager. And if Berri does come here, they also cautioned, it could as well serve to confirm the apparent stalemate in negotiations -- and the predicament that he and Assad are in -- as provide a solution.

Bedeviling the Syrian efforts is the limited leverage that Assad and his ally, Berri, are thought capable of bringing to bear on the more radical Shiite elements in Lebanon, especially the Iranian-influenced Hezbollah, or Party of God, said to have hijacked the Americans' TWA airliner.

Nevertheless, some of the most experienced U.S. officials in Washington are known to feel that there are, at this point, only two possible breaks in the hostage crisis. One involves the possibility of Syria being able to influence the hijackers. The other involves a gradual conclusion by Israel that its relations with the United States are of overwhelming importance and that it should, therefore, grant Berri's demand and release the more than 700 Lebanese prisoners it is holding.

[These same officials suggest that both Gorbachev and Assad are concerned about the effect of a success for the extremist hijackers, fearing the strengthening of religious fanatics in both Syria and Lebanon. Assad, in this view, is also said to agree with Washington that the U.S. hostages should be released and that holding them is counterproductive in terms of freedom for the Lebanese prisoners, whom Israel had said were going to be released anyway.]

President Assad and Hojatoleslam Ali Akbar Hashemi Rafsanjani, influential speaker of the Iranian parliament, conferred here Sunday and Monday. No communique was issued after Rafsanjani left for Tehran today, but diplomats said they assumed that the plight of the hostages was discusssed along with other subjects.

In a news conference yesterday Rafsanjani condemned the hijacking of aircraft in general, and said that if Iran had known "that this would have happened we would have prevented it for sure."

However, he also insisted that, "I have no idea whatsoever about the identity" of the hijackers.

Analysts have not totally discounted the possibility that some hostages may be held by Shiite splinter groups with no known wider allegiances. They noted that much of the highly effective fighting mounted against the Israelis this winter and spring in south Lebanon was the work of such pickup groups.

But the presence of Sheik Mohammed Hussein Fadlallah among a group of visiting Lebanese Shiite clerics who conferred with Rafsanjani here raised hopes that such free-lancers were not involved.

Fadlallah, despite his denials, has been linked with the Hezbollah in Beirut ever since his name was first mentioned after the October 1983 suicide car bomb attacks that killed 241 American marines and 58 members of the French expeditionary force.

Syria's inability so far to free the TWA airliner hostages is not the first such setback. On June 12, two days before the airliner was hijacked after taking off from Athens airport, Assad publicly denounced the kidnaping of diplomats and confessed his frustration in being unable to free seven Americans and two French diplomats kidnaped in Beirut, despite a personal message from President Reagan asking him to intervene.

Assad's dilemma is yet another illustration of the difficulty outside powers have experienced in dealing with Lebanese clients whom the outside world often assumes to be perfectly disciplined and under control.

During the recent fighting between Syrian-backed Amal and Palestinians in the south Beirut refugeee camps, Druze leader Walid Jumblatt demonstrated his independence from his nominal Syrian ally. He allowed Palestinian gunners to use hills in his territory to fire artillery at Amal positions.

And if the Syrian Army in the Bekaa Valley still controls the Hezbollah and other Lebanese Shiite groups that are influenced by Iranian Revolutionary Guards -- who are also around that valley -- Syria has no military presence in Beirut and thus no way of exerting direct pressure on pro-Iranian elements there.

Moreover, whatever the present embarrassment caused by the Hezbollah and other Iranian-infleunced radicals, they still constitute a potent prod to Amal in achieving Syria's top priority of driving Israel and its surrogates of the South Lebanon Army out of all Lebanon once and for all.

In the past, such competition between rival Shiite militias also served Syria's purpose of preventing any Lebanese group from dominating the others and contesting the authority of Damascus.

Now Syria is apparently learning the lesson that many western governments had warned of when Assad became Tehran's principal ally in the Arab world: an alliance between the lay Syrian government and the revolutionary fervor of Shiite Iran could prove both embarrassing and eventually dangerous.

But whatever the appreciation in the West, that alliance still provides serious benefits for both parties.

Iran appreciates Syria's weight in Arab councils. And Syria not only benefits from a supply of cheap Iranian oil, but also enjoys a free hand in Lebanon thanks to the Persian Gulf War in which Iran ties down the Army of Assad's arch-enemy, President Saddam Hussein of Iraq.

In the balance, that alliance may count for as much, if not more, than the American hostages whose deliverance Assad seems genuinely committed to bringing about.