Saudis, Americans sing in tune behind the scenes?

Saudi Arabia is emerging ever more clearly as one of the key players in the formulation of US Middle East policy under the new Reagan administration. The Saudi role is a sensitive one. The Saudis have geography, oil, and money on their side in their efforts to influence American policy in their direction -- indeed, in the direction of the Arabs generally.

But the Reagan administration has on its side, in the application of leverage , the most effective military umbrella that can be offered the Saudi royal family, for whom the bottom line is survival.

Also in play on the American side is the pressure that pro-Israeli interests have learned to apply so effectively through the US Congress. At the moment this pressure is encouraging the argument within the United States that the Saudis must be made to offer a suitable quid for any quo they receive from Washington.

Out of this jostling could come closer, even if only tacit, Saudi cooperation with the US in developing a broad front to face the Soviet threat in Southwest Asia all the way from the Bosporus through the Gulf to the Khyber Pass and Pakistan. Already there are pointers in the direction of tacit cooperation between the US and Saudi Arabia in applying pressure to President Assad of Syria , whose isolation in the Arab world has driven him into a treaty of friendship with the Soviet Union.

Against this background should be seen the maneuvering in the wake of the latest upsurge of violence in Lebanon. This violence includes on the one hand an escalation of Israeli strikes against Palestinian bases in Lebanon; and, on the other, the fierce Syrian assault on the town of Zahle, a strategic Lebanese Christian stronghold.

Both Israelis and Syrians have been trying to make points for themselves at the very time when US Secretary of State Alexander M. Haig Jr. was making his first reconnaissance swing through the area since assuming office.

Significantly, while in the region, Mr. Haig took a public stand against the Syrians more hostile than was the US attitude toward them during the Carter presidency. This, of course, was satisfying to the Israelis, whose foreign minister had said Israel would not sit idly by and watch Syrians kill Lebanese Christians (who are for the most part pro-Israeli, anti-Syrian, and anti-Palestinian).

But beyond that, the US seems to be involving itself actively in considering alternatives to the now exclusively Syrian Arab Deterrent Force (ADF), which is nominally the principal peacekeeper between the warring factions in strife-ridden Lebanon. Significantly, there are signs that Saudi Arabia is being drawn into these US efforts.

There are reports that the Saudis have played a part in the latest cease-fire efforts in the Zahle area, where Lebanese Christians have been under Syrian attack. The leverage in Saudi hands is the considerable Saudi contribution to the funds that the Arab League has been advancing to the Syrians to help meet the cost of the ADF in Lebanon.

The French newspaper Le Monde pointed out last week that when Arab foreign ministers last December renewed the ADF mandate for six months and voted funds for it, many of them had reservations and Saudi Arabia actually abstained. Le Monde raised the possibility of the Arab foreign ministers withholding funds from the ADF when the mandate comes up for renewal in June.

Alongside this should be seen the current visit to the Middle East of United Nations Undersecretary General Brian Urquhart, now in Israel after several days in Lebanon discussing the problems of the United Nations Interim Force in Lebanon (UNIFIL) in the south. Mr. Urquhart, though chiefly concerned with UNIFIL, is thought to be also discussing the overall question of peacekeeping throughout Lebanon.

All of this is provoking angry comment from Soviets, Syrians, and Palestinians.

The Soviet news agency Tass has blamed Washington "and its allies in Tel Aviv and Cairo" for events in Lebanon. The Syrian government newspaper Al Baath said Syria strongly rejected "the call made by France and the US to internationalize Lebanon and for a UN force to interfere in its affairs."

Palestine Liberation Organization (PLO) spokesman Farouk Kaddoumi accused the US April 12 of adopting a "hostile, offensive policy in the area." He called on the PLO to reinforce its ties with the "camp of friends," defined by him as the communist states led by the Soviet Union.