Millions of Iranians demonstrated throughout the country today in response to revolutionary leader Ayatollah Ruhollah Khomeini's call for a campaign to liberate Palestine and "drown Israel with buckets full of water."

The massive turnout of Khomeini supporters came as Kurdish forces inflicted new setbacks on the government in the northwest border regions.

Pars, the official news agency, said an Iranian F4 jet fighter was shot down and another crashed during heavy fighting between government forces and Kurdish rebels near the border town of Paveh.

The marches in Tehran were both pro-Palestinian and anti-U.S. Crowds chanted, "Death to Carter, Begin and Sadat."

The crowds offered mass prayers for the restoration of Palestinian rights after the ayatollah had declared today -- the last Friday of the holy month of Ramadan when Moslems pray to cleanse themselves spiritually -- "liberation of Palestine day."

Khomeini said yesterday that "if every Moslem were to pour a single bucketful of water on Israel it would be drowned by an uncontrollable flood." He had urged Moslems all over the world to join in prayer today to coordinate their actions "to cleanse themselves of Zionism and free Palestine."

Apart from the millions in Iran, Moslems in other Islamic countries including Pakistan, Kuwait and Syria supported the ayatollah's campaign.

Syria made its physical presence felt in the Iranian rally for Palestine when its visiting foreign minister, Addul Halim Khaddam, delivered the keynote speech at the culmination of the march in Tehran of hundreds of thousands representing all shades of the Iranian political spectrum.

Accompanied by Iranian Prime Minister Mehdi Bazargan, leading Tehran clergyman Ayatollah Taleghani and Arab ambassadors, Khaddam declared that the Iranian revolution had a great and vital role to play in harmonizing forces in the Middle East for the battle to free Palestine.

He said the United States wanted to turn President Anwar Sadat of Egypt into "a gendarme to defend American interests in the Middle East."

But despite the massive feeling for the Palestine cause Khomeini generated among the Iranian people, there was still no sign of any material assistance in the fight against Israel.

Observers said all the rhetoric and verbal support paled in the light of the quick and vehement denial by the Iranian foreign ministry yesterday of a report that Iran had promised to send troops to Syria to fight on Israel's eastern front.

A foreign ministry spokesman said the reports had arisen from a Kuwaiti newspaper's misquoting Khaddam.

Meanwhile, two government Phantom jet fighters and helicopters were hit by Kurdish ground fire as renewed violence in western Iran escalated yesterday into house-to-house fighting in the town of Paveh near the Iraqi border.

The death toll in three days of fighting in the town approached 50 as Kurdish tribesmen attempted to mop up the remaining government security forces in Paveh and the government, unable to get ground reinforcements into the area, threw its air power into the battle.

[Iranian state television reported that at least 40 government guards had been killed and a deputy prime minister, Mehdi Chamran, was trapped with a small group of defenders in a military garrison on the outskirts of Paveh. The report said they were surrounded and all hope was lost.]

Two F4 jet fighters were hit; one crashed into rugged mountains and the other limped back to base, riddled with bullet holes. A Kurdish spokesman said the planes had been struck by automatic weapons fire during strafing runs on the tribesmen's emplacements in the town.