Israeli security forces were put on full alert last night and the entire coast south of Tel Aviv to Ashkalon was blockaded while flares lit up the night sky following reports that Palestinian terrorists had crossed the coast in a nightmare repetition of March 11 when 35 Israelis were killed in a terrorist attack on the coast road.

By the early hours of Monday morning, however, nothing could be confirmed and both police and army sources were beginning to believe that perhaps the reports were a false alarm. Security forces nevertheless were committed to checking throughout the night.

If nothing else, the incident proved that Israel today is taut and nervous following both the March attack and the Israeli invasion of Lebanon.

As far as could be rellably learned, a truck belonging to an export firm had reported by radio that a band of seven to 10 terrorists were attacking in an area southeast of Tel Aviv and that they had seized a truck.

Despite the nervous flash bulletins of news services, nothing could he confirmed by 2 a.m. this morning and it was not clear whether there were armed Palestinians loose again on the coastal plains or whether the entire country had jumped to a false report.