North Vietnamese troops mounted their first major counter-attack in Cambodia to-day (May 13) charging in waves through the barbed wire perimeter of an American base. Military spokesmen said 58 of the mostly teen-age attackers were killed against U.S. losses of one dead and eight wounded. The battle came as American headquarters was reporting the first withdrawal of U.S. troops from Cambodia involving an estimated 3,000 men. This morning’s attack was across the border. Strong Viet Cong elements were only 30 km. south of Phnom Penh with only a battalion of infantry and five French World War II tanks between them and the capital. The Viet Cong were applying pressure on several Cambodian towns, particularly Kampot, on the coast, and Kompong Cham and Takeo, respectively 120 km. and 80 km. from Phnom Penh, a military spokesman said in Phnom Penh. South Vietnamese land forces to-day launched a major thrust towards Phnom Penh aimed at opening the whole road between the Cambodian capital and Saigon.