MySpace is laying off nearly a third of its U.S. staff, or about 420 employees, as the once highflying Internet business tries to rein in costs and contend with fast-growing rival Facebook Inc. The cuts will leave the social-networking site with about 1,000 employees in the U.S. MySpace declined to say whether it is also cutting back its international operations, in which the company has invested heavily in recent years. No word on how many jobs will be cut overseas.