THE director of Hong Kong Polytechnic is suing the pro-China magazine Window for libel over three articles and a cartoon. Professor Poon Chung-kwong and the council of the Hong Kong Polytechnic yesterday issued a writ against the magazine's publishers, Asian Regional Projects Limited. The first feature appeared on April 15 this year. It was run under the headline: ''Poly lurches from crisis to crisis - special panel's standing questioned.'' The two other articles in question, published in May, were headlined: ''Poly perks raise eyebrows - allegations surface over junkets and payments'' and ''Ivory basement - Hong Kong poly's story only gets worse'', which was accompanied by a cartoon. A polytechnic spokesman refused to comment on the libel action or the contents of the articles.