The Hennepin County Public Library system is becoming embroiled in a debate over sexually explicit web sites after a complaint school children were viewing adult material in the libraries. A sub-committee of the library board is expected to discuss next week a citizens proposal to block internet pornography sites from library computers. Minnesota Public Radios Eric Jansen reports: Hennepin County has 60 computer terminals with internet access spread through its 26 branch libraries. Patrons can sit at those terminals to research databases and other World Wide Web sites, or simply, "