PHILADELPHIA, PENNSYLVANIA- Government health officials are wrestling with a tough decision: Should they approve the most ambitious clinical trials to date of an AIDS vaccine, even if the two candidates have clear shortcomings? At a meeting here last week, the U.S. military and the U.S. National Institutes of Health unveiled detailed plans to launch phase III "efficacy trials" next year of nearly identical vaccines. But, as a vigorous debate here indicated, some researchers have deep reservations about whether these tests should go ahead.