tKeep Up Pressure on MarinesReds Hit StrongpointsSAIGON (AP)Communist! Gio Linh and Con Thien, sev-gunners hammered three U.S. en miles apart and only 2,000Marine strongpoints just below yards south of the zone, formthe demilitarized zone Thursday, pouring in both rockets and mortar shells to keep up the pressure on the Leathernecks guarding against North Vietnamese sweeps into the South.“Leatherneck Square,” a Marine command post at Con Thien, came under mortar attack Wednesday night.A Marine spokesman said ♦here were no immediate reports on U.S. casualties in Thursday’s attacks on Marine strongpoints at Dong Ha, Gio Linh and Camp Carroll.A Marine spokesman said 200 rounds of both 140mm rockets and 82mm mortars crashed in on the forward headquarters of the 3rd Marine Division at Dong Ha, 11 miles south of the border zone between the two Vietnams.The barrages against Gio Linh, Dong Ha and Camp Carroll began at about 3 a.m. and ended shortly after 4 a.m.the top cornerposts of “Leather neck Square,” and the artillery position at Camp Carroll and the Marine command post at Dong Ha form the southern corners.U.S. Marines and North Vietnamese regulars hammered at each other Wednesday in set-piece fighting below the zone while U.S. fliers sought to knock out the enemy’s heavy weapons.The U.S. Command announced Marine fliers Tuesday night bombed two surface-to-air missile sites that reconnaissance showed the Communists were setting up within the DMZ.Bomb Gun SitesThe attack on these bases followed up U.S. Air Force strikes reported to have destroyed two and damaged another of the long-range 130mm—5.1-inch — guns shelling American positions across the border buffer i territory.High U.S. officers said that, though the SAM is a bulky weapon nearly 40 feet long, the North Vietnamese may be actually trying to infiltrate some mobile missile launchers into South Vietnam itself to hamperallied air operations.Soviet-made 140mm rockets exploded at Gio Linh, a forward base of Marines and Army artillerymen two miles south of the DMZ, in the long-range duelling. U.S. artillery and planes pounded enemy positions.Gas Not Confirmed Marine companies, attempting again to root North Vietnamese regulars from bunkers and tunnels near Con Thien, ran into heavy small arms and mortar fire late in the day.One company radioed: “We’re being gassed.This could not be confirmed, though the enemy, like American and South Vietnamese forces, has occasionally used ear gas. U. S. combat equipment includes gas masks.RaSUdtlnrStola:clt;trt!aitldtosIt(