The White House said today that the attack on U.S. Marines in Beirut was an outgrowth of Syria's refusal to withdraw its military forces from Lebanon and of Syrian influence over warring religious factions there.

A senior administration official, who asked not to be identified, said Syria has taken on the "spoiler role" in Lebanon "with encouragement from the Soviets."

At the same time, President Reagan accepted the recommendation of a quickly assembled group of senior officials, chaired by Vice President Bush, that the United States make "no change" in the size, scope or responsibilities of the 1,200 Marines in the multinational peace-keeping force on the ground in Lebanon.

Calling the Marines' presence "an essential ingredient of U.S. policy," White House spokesman Larry Speakes said, "The Marines are there playing a critical role . . . . It is our intention they will stay there to perform a peace-keeping role."

Despite their pointed criticism of Syria, administration officials took the position that the killing of two Marines in Beirut was what one called "a tragic but isolated incident" they hope will not be repeated.

After reviewing reports from Beirut, officials tended to conclude that the Marines probably were hit by fire intended for nearby Lebanese army forces. The officials said they hoped that better communications with the various armed factions in Beirut would help to avert more incidents.

If the Reagan administration can make the case that today's attack was an "isolated incident," it will be under less pressure to respond to calls to invoke a provision of the War Powers Act that theoretically would give Congress a veto over the Marines' continued deployment.

Whenever the president concludes that American forces abroad are involved in or facing imminent hostilities, the act requires him to report it to Congress, which then has 60 days to decide whether to order him to withdraw the troops.

Among those calling for such action today were Rep. Clement J. Zablocki (D-Wis.), chairman of the House Foreign Affairs Committee, and Sen. John Glenn (D-Ohio), a presidential contender. Sen. Barry Goldwater (R-Ariz.), normally a supporter of Reagan administration policy, went further and said the Marines should be brought home immediately.

However, the power of Congress to order the Marines withdrawn appears to have been blocked by the Supreme Court decision earlier this year that nullified so-called "legislative veto" clauses like the one in the War Powers Act.

The special situation group of senior officials that Bush chaired in Washington also ordered, with Reagan's consent, a "legal review" of the War Powers Act to "ensure that our reporting is consistent with the requirements of the act," Speakes said. When the Marines were sent to Lebanon last summer, the White House said it did not anticipate imminent hostilities.

Speakes said today he "would not" describe the current situation in Beirut as "continuing hostilities." But he added, as the administration has before, that it cannot guarantee such an incident would not occur again.

Reagan, who is vacationing at his ranch near here, conferred by telephone conference call for 14 minutes today with the special situation group officials, who included Defense Secretary Caspar W. Weinberger and Secretary of State George P. Shultz. Joining in the conference call were White House national security affairs adviser William P. Clark and presidential counselor Edwin Meese III, who were at at temporary White House offices here.

Speakes said Reagan's special Middle East envoy, Robert C. McFarlane, will visit Israel Tuesday to discuss "cooperative measures" between Israel and Lebanon to "assure" Lebanese government control of the Chouf Mountains area that Israel plans to evacuate in a redeployment of its troops in Lebanon.

A senior administration official said there are "discussions going on" about a possible U.S. request to the Israelis to delay the planned evacuation of the Chouf. Speakes refused to comment on this possibility, however.

Speakes also said that the special situation group recommended, and Reagan accepted, that a "key element" of U.S. policy continue its support of the Lebanese government.

Reagan telephoned relatives of one of the slain soldiers, Staff Sgt. Alexander Ortega, 25, of Rochester, N.Y. He also planned to telephone relatives of the other Marine, Second Lt. Don Losey, 28, of Winston-Salem N.C., Speakes said.

The Reagan administration stopped short today of claiming that Syria was directly responsible for the violence that killed the two Marines. But officials were strikingly critical of Syria in both public and background statements.

After consulting with senior administration officials, Speakes said, "The latest fighting points to the urgent need for Syria to work out its own withdrawal with the Lebanese government." Responding to questions, he added that, "The Syrians' refusing to withdraw is certainly a complicating factor that has had an effect on the situation there."

Speaking on condition he not be identified, another official said, "It's obvious the Syrians have motivations," which he described as preventing the Lebanese army from moving into positions evacuated by the Israelis in the Chouf Mountains. He also said the Syrians "could be" seeking the withdrawal of the contingent of U.S. Marines in the multinational peace-keeping force.

"It is quite evident that the missing link in the peace process is Syrian refusal to . . . withdraw," Speakes said, adding that there is "no misunderstanding" the close relationship between the Syrians and the Soviets or the Syrian influence over warring religious factions in Lebanon.

Questioned about the basis for this claim, Speakes said, "The statement is not made lightly."

Another official said McFarlane is attempting to convince one religious faction, the Christian Druze, to allow the peaceful deployment of Lebanese armed forces in the Chouf Mountains when the Israelis leave. McFarlane met in Paris on Saturday with Walid Jumblatt, the head of Lebanon's Druze community, to discuss this.

The administration official said Jumblatt wants assurances that the Druze will not suffer for laying down their arms when the Lebanese army takes control. Jumblatt's "real next step" is to consult the Syrians, the official said, and the administration says it fears that Syria will urge the Druze not to allow the Lebanese army to move in peacefully.

Although McFarlane was reported to have had "encouraging" talks with the Druze leader in Paris, the Druze artillery joined Shiite Moslem guerrillas in attacking the U.S. Marine and Lebanese army positions in Beirut, according to an official here.

The official said it was difficult to explain why the Druze had joined in the attack. He added that the attack had been led by the Shiite Moslem guerrillas "supported" by Druze artillery.

Speakes attempted to draw a distinction between McFarlane's talks in Paris and the violence in Beirut. The violence, he said, was a situation "that is taking place in a specific area on the ground."

The two Marines were the first combat casualties since U.S. Marines were dispatched to Lebanon Aug. 25, 1982, in the aftermath of the Israeli invasion. A Marine was killed last fall defusing bombs in the area.

Reading a statement to reporters after talking to Reagan by telephone, Speakes said, "We are shocked and grieved by the deaths of the U.S. Marines in Lebanon."

"We condemn those who are responsible for the continuing violence which has claimed many victims, including our own Marines," he said. "Once more, we call on all elements to end this senseless violence and unite behind the Lebanese government to restore national harmony."

"It is our intention that they the Marines will stay there to perform this peace-keeping role that they were sent there, and that they have been largely successful in doing," Speakes said. Reagan was awakened at 1:55 a.m. California time by Clark and told of the killing of the Marines, according to Speakes, who said Reagan "expressed profound sorrow" and called the deaths "tragic."