Egyptians were confronted today with dramatic pictures of the assassination of President Anwar Sadat that suggested Egypt's security force, rated perhaps the best in the Arab World, failed to offer Sadat significant protection when his assailants struck yesterday.

The pictures, published today in the daily newspaper Al Akhbar, formed a major element in the questioning here of how the assailants put ammunition aboard a parade truck and then got the truck assigned to the inside lane near the reviewing stand where Sadat was killed.

Egyptian sources say security personnel worked three days before the parade inspecting the participating soldiers, their weapons and every truck and tank that took part in celebrating the Egyptian capture of the Suez Canal on Oct. 6, 1973.

Questions being raised here cast doubt on the government's assertion tonight that there were only four assassins acting alone. But it is the news photographs that are doing the most damage to the reputation of the U.S.-trained presidential bodyguard that had accompanied Sadat into the stadium and then seemed to disappear at the moment of attack.

Al Akhbar's photographs show four men armed with automatic rifles running toward the reviewing box where Sadat and other top government and military figures were seated.

Not a single security man or soldier stood between the assailants and the presidential box. There is no sign of any others present anywhere around it, although one does appear to have been firing from behind the stand.

Two of the assassins can be seen in one picture standing on their tiptoes to reach over the front wall of the reviewing stand and fire virtually point-blank at a pile of chairs beneath which Sadat was lying.

The pictures indicate, and several foreign television cameramen confirm, that instead of rushing to block the way of the assailants, Sadat's security personnel ran away and took cover. This gave the assassins a clear passage and allowed them to approach within only a few feet of the president.

There was no official explanation today of why Sadat's security guards acted in this manner. Sadat may have been already mortally wounded by several grenade explosions and the initial burst of gunfire from the assailants.

They were riding aboard a truck that was hauling a heavy artillery piece past the reviewing stand and they opened fire before jumping out.

Before the incident occurred, the area in front of the reviewing stand was full of both military and police security personnel as well as photographers filming the parade and the president.

Both the Al Akhbar photographer Makram Karim and CBS cameramen Richard Jeffery stayed to take pictures of the assassination while the security men fled.

The only gesture of protection offered Sadat that can be seen in the pictures is from several plainclothed bodyguards or officials throwing chairs over the fallen president in a vain effort to save his life.

According to the account of the semiofficial newspaper Al Ahram, Gen. Abel Halim Abu Ghazala, defense minister, and Fawzi Abdel Hafez, the president's private secretary, were the two officials who did the most to try to save the president, mainly by bringing him to the ground and placing their chairs over him.

But the president, the newspaper said, had first tried to stand up instead of lying down and both he and Hafez were then hit. The account said the president's guards exchanged fire with the assassins, killing one of them and capturing four others -- a discrepancy with the later account of four assailants.

Egyptian security has heretofore been rated as one of the best in the Arab world. The presidential bodyguards are instructed by the U.S. Secret Service and spend one year in on-the-job training in the United States before taking up active duty at home.

When Sadat arrived at the parade, his limousine was flanked on either side by three bodyguards standing on running boards while two others held onto railings at the back.

Where these eight bodyguards were as the shooting broke out is not clear, but they did rush, once the shooting tapered off, to get Sadat out of the stand and into a helicopter waiting behind it.

In defense of the security force, eyewitnesses noted that the attack lasted no more than several minutes and that initially everyone's eyes were fixed on Mirage planes making dramatic passes just above the roof of the reviewing stand. This gave the assailants the initial element of surprise over the security.