Police Sunday reported no significant increase in violent crime despite the layoff of 690 officers Friday. The layoffs, designed to save the city $27.6 million over the next 10 months, involved nearly 1 of every 7 on the force. Since October, 1,100 officers have been laid off by the city in a move that Mayor Coleman A. Young, a black, says could virtually wipe out five years of affirmative-action gains in the department. An 11th-hour meeting between Young and the president of the Detroit Police Officers Association, failed to produce any major agreement on alternatives to the layoffs.