IF NEW YORK'S LIBERAL PARTY WERE TO BE OFFERED AS PROOF of the moral bankruptcy of fusion or third party endorsements of major party candidates, Eric Chester would have his case secure. Unfortunately, since the suppression of Socialist Party campaigning by various legal and illegal means during 1917-20, the odds against Left candidates winning have been so long that liberal-leftish Democrats with good records on U.S. intervention, labor, women's issues, racism and the environment have drawn leftwing support and almost certainly will continue to do so--irrespective of arguments against the ultimate logic of such support.The Supreme Court has recently made Chester's case stronger, ruling that states may properly bar third party endorsements or fusion tickets. But experiments will continue, and at best will provide useful lessons, good and bad. More than that we cannot say without resorting to dogmatic pronouncements.