Israel, responding to reported Syrian troop maneuvers near the Golan Heights, has put some of its military units on a higher state of alert and warned the Syrians today that isolated clashes between the forces could escalate into full-scale war.

The warning to Syria that Israel will not necessarily limit its military response in case of a clash was voiced by several officials, including Foreign Minister Yitzhak Shamir as he left the country on a trip to Europe.

Shamir said Israel is taking "all necessary precautionary measures" and hopes that Syria "won't make a fatal mistake." If hostilities occur, he added, Israel "will determine the rules of the game."

In Washington, the State Department issued a statement saying that the recent Syrian buildup in Lebanon and along the Syrian-Lebanese border "could threaten the uneasy peace that now prevails in Lebanon." It urged "those who are exacerbating the tensions to exercise the utmost restraint so that the risk of a conflict can be reduced."

The statement also called on all foreign forces in Lebanon to make "a timely withdrawal." Israeli officials have said that their government has asked the United States to pass messages to Syria urging Damascus not to raise tension.

Israeli military sources confirmed that some Israeli military units were placed on alert yesterday in response to Syrian maneuvers near the border between the two countries on the Golan Heights, which Israel captured from Syria in the 1967 Middle East war and annexed in December 1981.

The sources characterized the alert and other undisclosed Israeli measures as "very low profile" and said there had been no significant new troop mobilizations or reinforcement of Israeli units either on the Golan Heights or in southern Lebanon.

However, journalists returning from an Israeli guided tour of front-line positions in Lebanon's Bekaa Valley yesterday reported seeing large numbers of Israeli tanks, armored personnel carriers and other military vehicles traveling north through the occupied West Bank toward the Golan Heights.

Beirut radio stations said Lebanese officials reported that 250 Israeli tanks and armored personnel carriers were seen heading to the Bekaa from southern Lebanon Thursday and Friday, The Associated Press reported.

State-run Damascus radio said Israel "has sent huge military reinforcements to Lebanon" and added that Israel's military measures "could be described as provocations or even direct challenges to Syrian forces stationed in Lebanon," Reuter said.

The Israeli warning and apparently limited military alert added to the tension with Syria that has been growing since the signing on May 17 of the Israeli-Lebanese troop withdrawal agreement. But Israeli officials continued to insist they would do everything possible to avoid a clash with Syria and would not allow themselves to be "provoked" into hostilities.

In a speech in Tel Aviv today, Defense Minister Moshe Arens said that a statement by Damascus that all Syrian military moves were defensive in nature was "good news" if true. Arens accused the Syrians of seeking to block implementation of the troop withdrawal accord in order to destabilize the Lebanese government of President Amin Gemayel.

"We shall do what has to be done," he said. "We will not be dragged into hostilities."

Syria adamantly opposes the Israeli-Lebanese agreement, charging that it rewards Israel for its invasion of Lebanon last June by granting the Israelis political and security advantages. Since the signing of the accord, the Syrians have beefed up their forces in Lebanon and along the Syrian-Lebanese border, where they now have about 50,000 soldiers, according to the Israelis.

There have been a number of isolated recent incidents involving Israeli forces, including one Wednesday in which Syrian jets fired air-to-air missiles at Israeli planes that were on a reconnaissance mission over eastern Lebanon.

Israeli officials have said consistently that they view the Syrian moves as part of a political and psychological war of nerves designed to subvert the troop withdrawal agreement and not as a prelude to a deliberate initiation of hostilities. That continued to be the prevailing view, although officials seemed less certain about Syrian intentions and more fearful about where events may lead.

Prime Minister Menachem Begin briefed leaders of the opposition Labor party on the situation today. Following the meeting, former prime minister Yitzhak Rabin said he remained convinced there would not be a war with Syria but that Israel was right in being on the alert.

In issuing today's warning, both civilian and military officials used the same phrase in asserting that Israel will not be bound by Syria's "rules of the game" by confining itself to responses to individual, isolated incidents if they continue and grow more serious.

"If they are talking about local skirmishes or a war of attrition, we don't want to play that game," one official said. "They won't dictate where or when or what kind of conflict there is."

Military sources said the decision to heighten the alert status of some units resulted from the "cumulative effect" of recent Syrian moves, saying that the most potentially ominous action was the beginning of the maneuvers south of Damascus yesterday.

The sources characterized the exercise as "large-scale" and said it involved ground forces, surface-to-air missile batteries, air units and artillery. Officials said there was no evidence that the exercise was anything but what the Syrians claimed, but added that the Syrians were in position to mount an attack quickly and that their intentions may not be clear for several more days.

Military officials also said that in recent weeks Syria has prepared new launching sites for surface-to-air missile batteries in Lebanon's Bekaa Valley. They said that no missile batteries are now inside Lebanon but that missiles could be moved quickly into Lebanon from just across the Syrian border.

The movement of Syrian surface-to-air missile batteries into Lebanon would almost certainly bring an Israeli military response. Last fall Israeli jets knocked out several of the Soviet-made missile batteries, and the military command declared that Israel "is determined not to allow the Syrians to bring surface-to-air missiles into Lebanon."

In the first Syrian comment on Wednesday's air incident, Syrian Defense Minister Mustafa Talas said in Damascus Thursday night that the Syrian Air Force had intercepted Israeli jets when they "violated the air space of Syrian forces" in Lebanon, Reuter reported.

"There was no combat in the real sense of the word," he told the official Syrian news agency SANA. He did not mention the firing of any missiles.