It was a plot that Allstair Maclean would be hard-pressed to match.

A cargo ship loaded to the gunwales with seven tons of high explosives approaches the coastline at full speed and suddenly unleashes a salvo of 45 Katyusha rockets. The captain locks the steering mechanism to head the vessel toward a fuel depot, and the seven-man crew jumps overboard and into a rubber dinghy to make a daring escape.

As the sailors race to safety, The rockets slam into the crowded seaside town, and the ship and fuel depot explode in an enormous conflagration, spreading panic in the enemy camp for miles around.

The plot, however, was not the stuff of which a good novel is made, but a Fatah terrorist raid which Israeli's government says was foiled Saturday when an Israeli naval patrol boat sank a bomb-laden freighter off the Sinai Peninsula coast about 20 miles north of the Straits of Tiran.

The Israeli defense forces yesterday released details of the planned Palestinian terrorist attack on Eilat, at the foot at the Gulf of Aqaba, which authorities said originated in the Syrian port of Latakia.

According to the government's account, the 50-yard-long cargo vessel, bearing a Cypriot flag but owned by a Fatah front organization, was spotted at 3:30 p.m. by an Israeli patrol board headed north toward Eilat.

The ship, named Agios Demetrios, aroused the suspicions of the Israeli crew because of what appeared to be rocket launcheers covered by tarpaulins on her decks. Navy officials said the Agios Demetrios failed to stop when ordered, and, when warning shots were fired over her bow, attempted to ram the Israeli boat.

The Israelis opened fire on the vessel, causing some of the munitions to explode, resulting in injuries to three of the seven Fatah crewmen, government officials said.

The crew of a second Israeli boat boarded the freighter, authorities said, and found its hold stuffed with explosives and detonators and its deck crammed with Soviet-made Katyusha rocket launchers primed and ready for firing.

As the Israelis were rounding up the Fatah crew, the explosives in the hold began to burn, and shortly afterward the Agios Demetrios exploded and sank, officials said.

Israeli authorities said the terrorist squad was led by Fatah Maj. Abdullah Jaloud, whom they identified as a rocket specialist. One of several explosives experts aboard the ship, military officials said, had been a commando instructor for the terrorist squad which raided the coastal road near Tel Aviv last March, killing 37 persons. That raid triggered Israeli's retaliatory invasion of Lebanon.

Interrogation of the crew, authorities said, disclosed that Saturdays plan was to fire the rockets toward Eilat, whose beaches were crowded with thousands of campers there for the Rosh Hashanah holiday weekend.

The government said that early in September the Fatah unit arrived from Lebanon at the Syrian port of Latakia, where they were met by a man known as Abu Nizar, local Fath agent. The crew members allegedly told their israeli interrogators the ship was outfitted at Latakia with rocket launchers, and that two weeks later the craw received a briefing by the head of Fatah's military section, known as Abu Jihad.

On Sept. 21, the ship reached the Tripoli area of Lebanon, where shore boats loaded her with explosives and rockets. The Agios Demetrios than set sail for Port Said, passing throught he suez canal toward the Gulf of Eilat.

In releasing details of the plot, Israeli officials repeatedly mentioned the connection of Syria, whose army is engaged in major battles with Israeli-supported Christian militias in Beirut.

Israeli government leaders are currently engaged in intense strategy sessions, discussing how Israel can aid the Christian forces without scuttling the Camp David peace agreements and the final round of Egyptian-Israeli talks scheduled for Oct. 12.

On Sunday night, the Palestinian news agency claimed that a terrorist vessel inflicted heavy damage and causualties in an attack on military installations south of Eilat and had sunk several Israeli ships anchored there. It said two crew members were killed and seven captured.

Since the Camp David agreements, Israel has been the target of increased terrorist bombings, and officials say they expect more as Egypt and Israel near a treaty signing.

On Saturday, a bomb exploded outside the Union Bank of Israel in downtown Jerusalem. Earlier, a bomb was exploded on a crowded beach in Yamit, on the Sinai coast. There were no injuries in either incident, but during the holiday period police were called out to examine hundreds of suspicious objects.