SOUTH VIETNAM REPORTED YIELDING MOST OF CENTRAL HIGHLANDS AREA; MAIN EVACUATION ROUTES CUT OFF
S Vietnamese Govt reptdly has decided to abandon most of central highlands, including Darlac, Pleiku and Kontum Provs, because area has become militarily indefensible; decision was made after 14 days of sharp mil reverses in area; 1 informant indicates Govt may attempt to retake Ban Me Thuot; other sources doubt that attempt will be made; there has been no indication of how swiftly Govt forces will leave highlands; some sources say Govt units are moving on little used paths and prov roads because 2 main routes out of area have been cut by N Vietnamese; decision to abandon area reptdly was made after Mar 14 when Pes Nugyen Van Thieu conferred with Maj Gen Pham Van Phu in Nha Trang; N Vietnamese troops have been bldg extensive road system in highlands since signing of Paris peace agreements in Jan '73; decision is expected to be stunning blow to natl morale though there have been no visible signs of dissent; 3 provs represent about 16% of S Vietnam's land surface and population of 500,000; natl population is 19.5-million; measure of success of regrouping operation reptdly will be number of troops and civilians who manage to escape to coast from highlands; Nguyen Tu, last correspondent known to be in Pleiku, described scene as 'nightmarish'; Saigon command spokesman Lt Col Le Trung Hien says situation will be 'very critical if enemy can cut vital routes permanently'; asserts that troop movements in highlands are being made for tactical reasons and are not withdrawal; illus of S Vietnamese troops helping villagers fell from attack 50 miles northwest of Saigon; map (L)