2 RUSSIANS ARRESTED BY F.B.I FOR SPYING
FBI Dir Webster announces that 3 Soviet citizens caught picking up classified documents have been arrested on espionage charges; 3, seized in Woodbridge, NJ, are Rudolf P Chernyayev and Valdik A Enger, employees at UN Secretariat, and Vladimir P Zinyakin, who is released after being identified as attache to Soviet Mission to UN with diplomatic immunity; FBI confirms that US Navy officer was informant who supplied Russians with information on Navy's underwater warfare projects after Navy sifted materials to screen out highly sensitive material; 3 reptdly were observed picking up material on at least 7 occasions beginning Oct 22 '77; case is said to be unrelated to recent defection to US of Arkady N Shevchenko, UN Secretariat's Under Sec Gen and superior of Enger; Chernyayev and Enger illus (M)