U.S. intelligence specialists in Washington say the roughly 5,000 Soviet military personnel in Syria are manning an extensive and layered air defense system.

Officials say Soviet pilots are flying Soviet-built jet interceptors of the Syrian Air Force. They also are manning the new SA5 long-range anti-aircraft missiles that were installed in Syria earlier this year, as well as some older SA6 and SA8 surface-to-air (SAM) missiles, according to the officials.

In addition, they say there is a ring of Soviet-built and -operated electronic countermeasures equipment, meant to jam the radars of any attacking Israeli aircraft, around the SAM installations. The installations are also said to be protected by Soviet soldiers.

The buildup of Soviet forces in Syria is cause for considerable concern here and in Jerusalem. However, U.S. intelligence specialists say there are no signs that either the Israelis or Syrians are moving toward any fresh outbreak of fighting.

The presence of Soviet troops, however, makes clear that in any new attacks, there could be significant Soviet casualties, and probably much higher Israeli losses than suffered in previous assaults on Syrian air defenses. That could create an unpredictable situation as far as greater and more direct Soviet involvement in fighting.