Yes, PAS is a Scrabble word!

Letter values in Scrabble US: P 3, A 1, S 1.

Is it a valid word?

PAS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

(ballet) a step in dancing (especially in classical ballet)
an informal term for a father; probably derived from baby talk
a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead
a unit of pressure equal to one newton per square meter
a Mid-Atlantic state; one of the original 13 colonies
an electronic amplification system used as a communication system in public areas

Also: atomic number 91, keystone state, public address system, p.a. system, pa system, p.a..

Not playable in Scrabble US: PAPPA, PROTOACTINIUM, PENNSYLVANIA.