*ECB OFFICIALS WORRIED MARKET STRESS MAY HINDER MONETARY POLICY
*ECB OFFICIALS WANT NEW INSTRUMENT READY FOR JULY MEETING
*ECB LIKELY TO OFFSET BOND-BUYING UNDER NEW ANTI-CRISIS TOOL
*ECB OFFICIALS WORRIED MARKET STRESS MAY HINDER MONETARY POLICY
*ECB OFFICIALS WANT NEW INSTRUMENT READY FOR JULY MEETING
*ECB LIKELY TO OFFSET BOND-BUYING UNDER NEW ANTI-CRISIS TOOL