An Army laboratory has identified the remains of six American service personnel missing from the Vietnam War, the Pentagon said. The six--all Navy aviators--were identified by the Central Identification Laboratory in Honolulu after the remains were returned by Vietnam with 17 others in November. More than 2,300 Americans are listed as missing in Indochina. All told, the remains of 178 Americans have been repatriated and identified since the end of the war. The Navy withheld two identities at the request of the families. The others were: Cmdr. Charles E. Barnett of Houston; Cmdr. Clarence O. Tolbert of Tishomingo, Okla; Lt. Cmdr. Robert T. Hanson Jr. of Toledo, Ohio, and Lt. Frederick M. Kasch of San Diego.