West Bank BarrierIsraeli officials said today that the attempted infiltration of the West Bank from Jordan by a band of El Fatah terrorists Friday constituted the most serious breach yet of the cease-fire agreement Israel entered in to last summer to end a spate of bloody warfare with the Palestine Liberation Organization in south Lebanon.

Three of the terrorists were captured yesterday in a clash with Israeli forces in which two of them were wounded. Two, and possibly three, of the infiltrators managed to escape across the Jordan River. The clash ended a two-day manhunt during which the infiltrators planted mines on roads used by Israeli patrols. There were no Israeli casualties.

The Cabinet was briefed on the episode today by Defense Minister Ariel Sharon but since it convened as a ministerial defense committee, no information was released.

Chief of Staff Gen. Rafael Eitan told a press conference here yesterday afternoon that the infiltration attempt was one of the most sophisticated tries yet made. He said that while one group of terrorists laid mines, a group of three heavily armed men made its way into hilly country with the intention to attack Jewish settlements in the Jordan Valley and on the West Bank.

Eitan said the mines were planted in order to hinder the dispatch of Israeli reinforcements to the region and to create the impression that mine-laying was the only purpose of the infiltration. He said the terrorists crossed into Israeli territory in the Beisan valley.

Tracked Down to Alon Moreh

Maj. Gen. Uri Or, commander of the central front, told the press conference that the terrorists were finally tracked down to caves north of Alon Moreh, a Jewish settlement on the West Bank. The weapons and explosives found on them were of Western, mainly American, manufacture of the type sold by the U.S. to Saudi Arabia and Jordan.

Eitan said he did not know if the weapons and explosives had been stolen or whether they were supplied to the PLO by Saudi Arabia or Jordan. He said the large quantities the infiltrators carried indicated that they may have been supplying other terrorist groups already in the area. Eitan said it was not known whether the Jordanians acquiesced to the passage of the terrorists through their territory or simply were unaware of their presence. In the past Jordan has acted to prevent such infiltration.

Army sources said the infiltrators were trained at a PLO encampment near Tyre in southern Lebanon by Syrian officers and entered Jordan by way of Syria. The PLO news agency in Damascus, Wafa, admitted today that three of its men had been captured. It denied that the infiltration was a violation of the cease-fire in south Lebanon because that region was not involved.