ONLY one of the eight companies involved in sweater anti-dumping investigations in the United States has responded to the surprise second round of questionnaires. Pettit and Martin partner Simon Luk, who has been advising some of the companies, said Hayward Knitters has been given an extension to next Tuesday to file its response. He believes the rest have ignored the questionnaires on the assumption they will be overturned by the US court. The second round of questionnaires, announced in May, stunned the sweater makers because it effectively went against a US landmark decision on anti-dumping, which was awarded in favour of Hongkong last November. In what was hailed as a major victory, the US International Trade Commission (ITC) reversed its earlier ruling that the territory had hurt American sweater manufacturers by dumping cut-rate products in the US. It was hoped that ruling, which came after a time-consuming and costly battle backed by the Hongkong Government, would clear the way for an end to the bitter three-year dispute which led to anti-dumping tariffs against Hongkong and other Asian sweater exporters. But the Americans showed they were determined to carry on the investigations in the face of this ruling with the release in May of a second round of questionnaires to the eight firms covering the period from September 1991 to August 1992. Mr Luk said: ''We have got an extension for Hayward, and they will answer. ''I guess many of them think the court case will overrule it, and so there will be no more outstanding investigations, but our client [Hayward] is taking the prudent measure that until it is overturned it should respond.'' He added that it was less time-consuming to reply to the questions a second time. It is expected the preliminary round of findings might come out in the middle of next month. Initially, questionnaires went out to the three exporters named by the US authorities - Comitex Knitters, Shanghai Knitwear and Wing Ho Knitwear - along with three unnamed firms, plus Hayward Knitters and LaMagma, which volunteered. They were backed by the Trade Development Council, which injected some $5 million into a $10 million fighting fund to pay legal fees. Exports of acrylic sweaters to the US have fallen significantly since the US anti-dumping action was initiated in 1989. according to Trade Department officials. The value of synthetic fibre sweater exports to the US, which totalled $809 million in 1989, slid to $564 million in 1990, the year dumping duties were imposed. The dispute began in 1989, when the US National Knitwear and Sportswear Association (NKSA) accused Hongkong, Taiwan and South Korea of dumping man-made fibre sweaters at below cost to capture the US market.