Special U.S. envoy Philip C. Habib today flew back to Israel, rather than Syria as expected, amid speculation that his Middle East peace mission is heading into a stall despite earlier suggestions of a breakthrough.

The meager visible results of more than two weeks of shuttle diplomacy seemed to indicate that the Habib mission's principal virtue is becoming a play for time, keeping him in the area to allow Syria and Israel to reflect on the costs of war on the assumption neither will begin hostilities while the U.S. peacemaker is still shutting back and forth trying to prevent them.

Habib's decision not to go to Damascus was seen in the light of Syrian officials' statements that he was welcome back, but only when he had new proposals. In addition, the official Syrian government newspaper, Tishrin, seemed to harden the rhetorical tone in Damascus today by warning that any board Israeli attack in Lebanon or Syria will draw retaliation "deep inside Israel."

The editorial coincided with a warning on the official Syrian radio that "there are many indiacations that Israel has the intention of launching a full-scale aggression against Syria . . ." One indication cited by the radio was a Syrian report that Israeli reconnaissance craft are flying missions over Syria proper in addition to their surveillance of Syrian positions in Lebanon.

[A gathering of Arab League foreign ministers in Tunis, meanwhile, affirmed total support of Syria in case of Israeli attack and warned the United States that if it continues support for Israeli it risks "serious conflict" with the Arab world. But the ministers' resolution, reached in the early hours today after prolonged discussions, did not seem to apply to Syrian missiles within Lebanon, the main cause of the crisis. It referred only to aid in case of attack on Syrian territory.]

[Diplomats at a meeting in Abu Dhabi of Persian Gulf countries seeking to organize gulf security cooperation said they, too, support Syria in the showdown. But they also pointed out the necessity of finding a way to reestablish Lebanese government authority for any long-term solution to the country's turmoil.]

Another possible cause for Habib's trip to Israel was to provide more time for Saudi mediation with Syria. In this context, observers noted that President Hafez Assad of Syria today dispatched his brother, Rifaat, to Riyadh with a letter for King Khalid. Its contents were not disclosed.

In what was seen as another sign that Habib was still seeking a successful tack, the Israeli state radio reported that Prime Minister Menachem Begin's weekly Cabinet session Sunday will set an "acceptable deadline" for Habib's mission. It did not add what delay Begin might accept.

Reports from Jerusalem said Habib met briefly and informally with Begin soon after his arrival. Emerging from their meeting, news agencies said, the envoy told reporters only that he is continuing his mission, adding: "You never give up." Begin did not make himself available for questions.

One obstacle facing Habib is Begin's apparent broadening of Israeli terms -- in a television interview Thursday -- for a peaceful settlement of the crisis. The Israeli leader said Syria must remove missiles recently deployed on Syrian soil near the border with Lebanon, in addition to those on Lebanese soil. In public at least, attention previously had centered only on those missiles within Lebanon, installed April 29 after Israeli jets shot down two Syrian helicopters used in an assault on Lebanese Christian militias.

Israel is likely to encounter more resistance to any attack on the missiles than it would have when the crisis began. The Syrians have reinforced protective missile systems in and around the SAM 6s positioned in Lebanon and other missiles in the border strip just inside Syria. Thus an attack today stands to be an operation more costly in lives and aircraft.

At the same time, Syria, despite the Arab world rallying to its previously isolated cause, would if war broke out go into the battle without Egypt, the most populous of Arab nations and generally credited with having its most effective army. President Anwar Sadat has signed a peace treaty with Israel and, fearful of not recovering the last slice of occupied Sinai, has let it be known that he would not follow the Syrians into war.