HE IS STANDING IN "SOFT DRINK PARLOR" WHEN STICK-UP MEN ENTER Chicago, Dec. 31— (P)— Michael Langan, a policeman in plain clothes, was killed last night by four bandits who posed as .policemen .policemen and held up a northwest side soft drink parlor. Langan was standing at the bar talking to the proprietor when the bandits entered. "Stick 'em up; we're policemen," one of them cried. Langan pushed toward them, firing firing as he went. The bandits fled to the door, returning the fire. Langan fell with a bullet in his head.