WASHINGTON( AP)bumpingAa line carrying flammable fluid caused the explosion and fire in a Titan II missile silo which killed 53 civilian workers near Searcy, Ark., Aug. 10, the Pentagon said Thursday night.Arkansas members of Congress received advance notice ol the cause. The Defense Department was scheduled to make an official announcement on the cause today.* * *Only two persons survived the blast in the gun barrel of America's mightiest defense missile.A thick stream of smoke inthe silo hampered rescue operations. It took about 20 hours for rescue workers to remove all tne bodies from the silo.Pentagon officials did not identify the welder in the report to the Arkansas congressional delegation.The Pentagon said everything possible is being done to prevent a recurrence of such an accident, the worst in the history of America’s space and missile program.The Pentagon also said it was doing everything possible to help the families of the victims.TTie 15 men in the silo at the time of the fire were non-federalemployees. They worked for various private firms under contract or sub-contract to the government.The workers were renovating the site in the government’s updating program at 54 such missile sites in the nation. There are 18 sites in the central Arkansas area, all controlled by Little Rock Air Force Base.A crack, 21-man Air Force investigation team probed the area for several weeks seeking the cause of the fire. There were no progress reports avail-abl on the investigation.Air Force Secretary Eugene Zuckert, Sen. John L. McClellan. D-Ark., Rep. Wilbur Mills, D-Ark., and Gov. Orval E Fm-bus of Arkansas inspected the of damage.iy