	bolt beranek bbn files for debenture offering bolt beranek and newman inc said it filed with the securities and exchange commission a registration statement covering a mln dlr issue of convertible subordinated debentures due a portion of the proceeds will be used to uire all of the outstanding capital stock of network switching systems inc another part will allow bolt to exercise its option to purchase all of the limited partnership interests in bbn rs expert limited partnership with the rest used for general corporate purposes the company named painewebber merrill lynch and montgomery securities as underwriters reuter 
