Among more than 100 Israeli soldiers killed during the first six days of the invasion of Lebanon was the intetnded next chief of Mossad, Israel's intelligence agency.

Prime Minister Menachem Begin disclosed today at the funeral of Maj. Gen. Yekutiel Adam, killed in a P alestinian ambush in southern Lebanon, that he had planned to call Adam into his office on Sunday and tell him of the apppointment.

Adam, one of the most popular officers on the Army's general staff, had been on a sabbatical to study in the United States when he was called back to participate in the Lebanon invasion. His last Army post had been deputy chief of stff, and he had been considered a leading candidate to replace Maj. Gen. Rafel Eitan as Army chief of staff.

The Israeli Army command said that Adam, 55, and reserve Col. Haim Sela were driving toward a field headquarters in southern Lebanon when they were ambushed by guerrillas. Both were killed.

Adam joined the Army after serving in the pre-independence Jewish guerrilla force, the Haganah, and in 1956 was commander of a rec onnaissance unit in the elite Golani Brigrade, after which he bacame coommander of retaliatory operations that were conducted against Palestinian guerrillas at the end of the 1967 war.

He later became commander of the Army's northern district, responsible for combating terrorist attacks along the border with Lebanon.

Defense Minister Ariel Sharon, in disclosing that more than 100 Israeli soldiers have died in the invasion, cited Adam and said that "many of the Army's best officers" had been among the casualties. Officer casualty rates have been high in all four of Israel's major wars in the last 34 years, partly as a result of the Israeli Armys's tradition that officers are expected to be at the front of their combat units.

Sharon said that more than 100 soldiers had been killed and 600 wounded in the current fighting, although this morning the Army ccmmand said that 68 had been killed in action, 424 were wounded, seven reported missing and one was known to be a prisoner of war.