When it comes to building a top-notch faculty, racing to land prominent scholars is only half the battle for colleges. The other half: Fighting off poachers intent on swiping the college's existing talented mid-career professors. At Cornell University, a $35-million gift announced by officials in late September will give the institution an edge in an increasingly competitive market for faculty members. It will be used for endowed professorships to be awarded university-wide. One of these positions has already been used to hold onto a prominent chemist who was being wooed by another Ivy League university. The money comes from Andrew H. Tisch, chairman of the executive committee of Loews Corporation and a Cornell trustee, and his wife, Ann. The Tisch University Professorships cover salaries and may also include money for start-up costs, graduate research support, travel and conference expenses, and sabbatical leave. The endowment, which can be allocated at the provost's discretion, is also designed to give Cornell the option to rebuild departments depleted by retirements and strengthen interdisciplinary fields, among other things.