A gas-filled balloon apparently manned by Palestinian guerrillas headed for the Israeli border crashed and burned in southern Lebanon, United Nations officials said today.

No trace of the balloon's occupants was found at the remote site near Majdel Islim, about seven miles west of the Israeli town of Kiryat Shemona. But U.S. authorities said they recovered automatic weapons, antitank grenades and plastic explosives from the burned wreckage of the balloon's gondola.

Timur Goksel, spokesman for the U.N. force in Lebanon, said that about midnight on July 21, there was reports of shootings and a bright flash of light in the vicinity, of Majdel Islim, which is controlled by a Ghanaian peacekeeping battalion. A patrol searched the rugged terrain, but found nothing, Goksel said.

Three days later, a Lebanese shepherd found the wreckage and reported it to U.N. officials. There was no explanation for the delay in reporting the incident.

Israeli Army officials said the balloon appeared to come from the direction of Syria, where the Palestine Liberation Organization maintains training camps for guerrillas.

"We know they have the technology capability in meterology to conduct such an operation. We assume from the weapons and ammunition that it was terrorists," an Army official said.

The Israelis, however, said they were not involved in shooting down the balloon. One possibility appeared to be the Christian Militia in southern Lebanon, who are supported by the Israelis.

A spokesman for the PLO in Beirut told the Associated Press, "I have no information whatever about this balloon business."