Special U.S. envoy Philip C. Habib flew to Saudi Arabia today and met with top Saudi leaders in an apparent effort to enlist that oil-rich country's help in easing the Middle East missile crisis.

Habib's first stopover outside the Beirut-Damascus-Jerusalem circuit, which he had made twice, came amid signs of mounting tension threatening his 10-day-old mission.

The U.S. Embassy here ordered official dependents out of Lebanon today and encouraged private Americans to leave, and the Lebanese prime minister called in the Soviet and U.s. ambassadors to seek their help in easing the crisis.

Although the State Department decision followed similar advice issued last month by the British and Austrian embassies to their respective citizens, in the heightened tension it was widely interpreted here as reflecting diminishing hopes in Washington that the missile crisis could be solved through diplomatic means.

With U.S. and Soviet fleets reportedly in the eastern Mediterranean and Syria standing firm, Habib's Saudia stopover took on new importance.

As a close ally of the United States and a major financer of Syria, Saudi Arabia is considered a major behind-the-scenes actor in the crisis that began April 29, when Syria moved surface-to-air missiles into Lebanon after Israeli jets downed two Syrian helicopters.

With U.S. influence in Damascus virtually nonexistent, Habib was reported by sources as varied as Israelis and lift-wing Lebanese newspapers to be trying to persuade the Saudis to fill the void.

As Safir, a usually well-informed lefist newspaper here, said the United States specifically wanted the Saudis to resume interrupted funding here for the Syrian-manned Arab Deterrent Force, which has an Arab League mandate to police Lebanon, in return for withdrawing the missiles.

Kuwait, Saudi Arabia and other oil-rich Arab states reportedly stopped funding the 22,000-man force in early January on the ground that Syria had failed to produce promised quarterly reports for the $180-million-a-year operation.

As Habib was landing in Saudi Arabia after an early-morning flight from Tel Aviv, official Riyadh radio said any threat to peace was not caused by the presence of Soviet-built missiles in Lebanon, but by "Israel's blowing up the importance of this fact."

In apparent anticipation of the American-Saudi talks, in Damascus the Syrian government newspaper Tishrin warned that the time had come for the Arab world to stand up and be counted in the confrontation with Israel.

"Neutrality is rejected and condemned," argued the newspaper of a government badly isolated in the Arab world less than a month ago, since "eventually it sides with the enemy."

"Silence, too, is cowardly neutrality," it added. "Either you are in the trench of Arab steadfastness," as the hard-line Arab front is called," or in the imperialist-Zionist trench," a normal code word for the U.S.-Israeli relationship.

Meanwhile, the U.S. Embassy here instructed the remaining nine dependents -- seven wives and two children -- of its staff to leave Lebanon and suggested that the 2,168 American residents should remain "only if they feel the need." Almost all that number are persons of Lebanese birth who have acquired U.S. citizenship.

Reflecting the Lebanese government's concerns about the tensions, Prime Minister Shafik Wazzan separately called in U.S. Ambassador John Gunther Dean and Soviet Ambassador Alexander Soldatov today to ask ltheir governments to "exert all pressure to prevent an explosion, restrain Israel and stand against aggression."

"I told the two ambassadors separately," Wazzan said, "that Lebanon did not want a new war on its territory."

Soldatov again clarified the Soviet position that its treaty of frendship and cooperation signed with Syria last October extends only to Syria proper, and not to Syrian troops serving in the Arab Deterrent Force. He described the situation as "dangerously tense."

Meanwhile, both the Palestine Liberation Organization and the Lebanese leftist National Movement formally proclaimed general moblilization. In fact, both organizations have been on maximum alert since fighting between right-wing Christians and Syrian troops in Lebanon broke out April 1.

Fighting was reported today on the key ridge line in the Mount Lebanon range around Mount Sannin, where Syrian control was invoked by Israel to justify its drowning of the two Syrian helicopters.

In Beirut, informed diplomatic sources said Libya has provided the Palestinian guerrillas with SA9s, a vehicle-mounted version of the shoulder-fired Soviet SA7 that has been in the guerrilla inventory for years.

Libya also was reliably reported to be providing the Sunni Moslem Morabitoun militia in West Beirut with six tanks, 22 armored cars, long-range artillery and 40-tube, truck-mounted rocket launchers.

Libyan leader Col. Muammer Qaddafi said yesterday in a ceremony marking the 33rd anniversary of Israel, "We tell America we are ready to supply the Palestinians with any weapon they can use."

He also called for a joint Arab military force equipped with modern air defense systems in southern Lebanon to confront Israel's preemptive strike policy.

Habib was said by U.S. officials in Riyadh to be planning to return to Syria Sunday.