BEST BETS NOT SO SQUARE.(LIFE & LEISURE)

BLUES

The Albany Visitors Center at Quackenbush Square alters its museum/tour-giving image when the city's venerable blues men, Ernie Williams and Mark Emanatian, perform an acoustic set at noon today. Bring your lunch. The music happens rain or shine. 25 Quackenbush Square, foot of Clinton Avenue, Albany. 434-0405. Free. Opening night CLASSICAL

The Philadelphia Orchestra's annual stay in Saratoga begins at 8:15 tonight with the program ``Yo-Yo Ma Special Concert.'' Charles Dutoit conducts and, you guessed it, the world's beloved cellist Yo-Yo Ma is the featured soloist. Works will include Beethoven's ``Leonore Overture No. 3'' and Dvorak's Cello …