The new commander of U.N. peacekeeping forces in Lebanon demanded today that the Israeli Army withdraw from southern Lebanese territory and suspend its support of Christian militia forces there, but Israel immediately rejected his demands.

Maj. Gen. William Collaghan spelled out his position during a meeting in Nazareth with top-ranking Israeli Army officers. He said Israel's presence within Lebanon and its support of forces led by renegade Lebanese Army Maj. Saad Haddad contribute to the instability that led to the deaths of three Nigerian soldiers of the U.N. Interim Force in South Lebanon (UNIFIL) during an artillery bombardment of a U.N. position Monday by the militias.

Maj. Gen. Avigdor Ben-Gal, commander of the Israeli Army's northern command, rejected Callaghan's demands "on the spot," according to a spokesman for the Army command. Ben-Gal warned that "changing the status quo" would endanger Israel's security and stimulate more fighting in southern Lebanon, the spokesman said.

The Army command described the atmosphere of the meeting as "quite tense" and said that Callaghan's attitude during this meeting was demonstratively unsympathetic."

Callaghan, it was understood, warned that European nations supporting the U.N. forces have given him a mandate to "act tougher" against Haddad's troops, whose rebel enclave along the border with Israel has been a major obstacle to U.N. forces ordered under a Security Council resolution to maintain order in the southern Lebanese hills and aid the Lebanese government in restoring state authority there.

Because of armed opposition from Haddad's Israeli-backed forces and Palestinian guerrillas, the U.N. troops have been largely unable to fulfill their mission since they arrived in southern Lebanon in the spring of 1978.

today's meeting came against the backdrop of heightened tensions in southern Lebanon over deployment of a 30-man Lebanese regular Army platoon in the town of Kantara, about eight miles west of the Israeli border town of Metulla. Haddad's forces been shelling Kantara after the town of Metulla. Haddad's forces been shelling Kantara after the Lebanese platoon moved in, defying Haddad's threats over the U.S.-owned Voice of Hope radio station that his artillery would open fire because of the Lebanese troops' presence. About 20 Nigerian soldiers were wounded in addition to the three killed.

Callaghan, an Irish officer who earlier this month assumed command of the 6,000-man UNIFIL forces, has ordered his troops to battle readiness whenever they come under fire from Haddad's militias.

[In New York, U.N. Security Council members were negotiating over the text of a statement to be made by the council president deploring the shelling and criticizing Haddad for the deaths. Knowledgeable sources said THE U.S. mission was opposing a draft statement that also criticized Israel for its support of Haddd, without also criticizing the Palestine Liberation Organization for its role in the southern Lebanon imbroglio].

Security Council Resolution 425 of March 19, 1978, calls on Israel to withdraw its forces "from all Lebanese territory" and assigns the U.N. forces to aid "the government of Lebanon in ensuring the return of its effective authority in the area." But Isreal views the Lebanese platoon's presence at Kantara as an attempt to extend Syrian influence in the Israeli-backed Christian enclave just south of the U.N.-controlled zone. Kantara itself lies in the U.N. area.

Callaghan today also demanded that Haddad's militias withdraw from four positions in southern Lebanon immediately. That demand also was rejected by Ben-Gal, who, according to the Army command, "emphasized the danger of changing the status quo, as well as underlinging the danger inherent in UNIFIL's desire to introduce new facts in the area."

The Israeli commond said the four positions control routes that Palestiman guerrillas regularly use in attempting to infliltrate to the Israeli border on terrorist raids.

Prime Minister Menachem Begin, in a visit yesterday to the northern Israeli town of Kiryat Shmona, said Israel had no part in Haddad's attacks on the U.N. positions in Kantara. He expressed regret for the Nigerians' deaths and said Israel will take steps to "prevent the recurrence of such incidents."

Deputy Defense Minister Mordechai Zipori said Isreal will continue to support Haddad, but will try to restrain him from shelling U.N. possitions. sHowever, Moshe Arens, chairman of the Israeli parliament's Foreign Affairs and Defense Committee, said Israel does not control Haddad, and can only exzpress its displeasure after the event.

Israel is the source of supplies, weapons and funds for Haddad's 1,500-man militia and 500-man regular army.