HAWKER SIDDELEY OFFER FOR CLAROSTAT <CLR> ENDS <Hawker Siddeley Group PLC>'s offer of 74 dlrs a share for all of Clarostat Mfg Co Inc's stock was scheduled to expire at 2400 EST yesterday. Company officials were unavailable for comment as to why the American Stock Exchange had stopped trading in Clarostat's stock for a pending news announcement.