An improvised grenade was thrown Saturday night at an Israeli military patrol on Rte 443 to Jerusalem near Maccabim. There were no casualties. The soldiers fired in the air. DEBKAfile: A high alert has been in force on Rte 443 since mid-week following intelligence of Palestinian terrorist gangs preparing to hit the passing traffic with firebombs. Over the weekend, large military and police forces were posted at close intervals along its length and senior politicians and officials ordered to use the alternative Rte 1 on their way in and out for Jerusalem.