Two Nigerian soldiers of the U.N. peacekeeping force in Lebanon were killed and 11 were wounded today during an artillery bombardment by Israeli-backed rightist militiamen and an Israeli Army Lieutenant was killed trying to dismantle a bomb planted by Palestinian guerrillas in a southern Lebanese village, U.N. and Israeli spokesman reported.

A U.N. spokesman said two Lebanese soldiers were also wounded when 25 shells landed on the village of Kantara, where a Lebanese Army force has been deployed along with units from the United Nations Interim Force in Lebanon, or UNIFIL.

The state-run Radio Lebanon said four persons, including a child, were killed in the shelling by Israeli-backed rightist militias under the leadership of Maj. Saad Haddad, who has called for removal of the Lebanese Army unit in Kantara. It also said that the market town of Nabatiyah, a stronghold of Palestinian guerrilla forces in southern Lebanon, was bombarded by Israeli gunners.

An Israeli spokesman in Metulla, just south of the Lebanese border, denied that Israeli artillery fired on Nabatiyah.

In Washington, the State Department reaffirmed support for the territorial integrity of Lebanon and said it is "deeply concerned" by the shelling of Kantara, adding:

"We . . . condemn these outrageous actions by Haddad forces which have caused the death and injury of UNIFIL personnel present in Lebanon under international mandate. There must be no interference with UNIFIL as it attempts to carry out its duties.".

Israeli military authorities said the Israeli Army lieutenant was killed and another soldier was wounded while helping Haddad's militiamen defuse time bombs placed by Palestinians in the village of Beit Lif, three miles north of the Israeli border.

A militiaman helping the demolition squad was also injured.