Threatening to detonate a bomb, a bank robber held up an American State Bank branch today at Albertson's grocery store at 50th Street and Indiana Avenue. No one was hurt and the robber took only a "small amount of money," said Greg Jones, a vice president at American State. The robber walked up to the bank counter — located near the western entrance of the store — at about 12:10 p.m. He was carrying an athletic bag designed to carry tennis rackets, according to police spokesman Bill Morgan said. The robber placed the bag on the counter and pushed it in the direction of one of the two tellers on duty. He then told the teller, "Gimme it all, chief," Morgan said.