In Commercial Markets, Mixed Signals
State of commercial real estate market in New York City examined; demand for office space is soft and rents are declining; investors are spending heavily for trophy buildings, but ignoring others; outlook for 2003 is unclear, with some real estate executives saying upturn in economy could have big impact and others saying upturn is nowhere in sight; large amount of sublet space pits tenants whose needs have diminished against landlords; office space vacancy rate in suburban markets of New Jersey, Fairfield, Conn, and Westchester, is rising and industrial sector has also slowed; hotels are drawing customers but cutting room rates to keep occupancy high; outlook is for occupancy to improve and hotels are trying to re-establish corporate relationships; photos; map (M)