Residents of Gary, Ind., voiced shock and anger over the drownings of five children who tried desperately to claw their way out of a slime-coated municipal swimming pool where they had gone in search of frogs. The four girls and one boy, from 6 to 13 years old and all related, drowned Sunday evening, officials said. The pool contained about five feet of stagnant rainwater at its deep end and the youths apparently slid into it. Mayor Richard G. Hatcher expressed “sadness and shock at . . . the tragic loss” and called a news conference for today.