Yes, REDUCING is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, D 2, U 1, C 3, I 1, N 1, G 2.

Is it a valid word?

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

any process in which electrons are added to an atom or ion (as by removing oxygen or adding hydrogen); always occurs accompanied by oxidation of the reducing agent
loss of excess weight (as by dieting); becoming slimmer

cut down on; make a reduction in
make less complex
bring to humbler or weaker state or condition
simplify the form of a mathematical equation of expression by substituting one term for another
lower in grade or rank or force somebody into an undignified situation
be the essential element
reduce in size; reduce physically
lessen and make more modest
make smaller
to remove oxygen from a compound, or cause to react with hydrogen or form a hydride, or to undergo an increase in the number of electrons
narrow or limit
put down by force or intimidation
undergo meiosis
reposition (a broken bone after surgery) back to its normal site
destress and thus weaken a sound when pronouncing it
reduce in scope while retaining essential elements
be cooked until very little liquid is left
cook until very little liquid is left
lessen the strength or flavor of a solution or mixture
take off weight

Also: cut down, cut back, trim down, trim back, bring down, come down, boil down, scale down, keep down, thin out, melt off, lose weight, slim down.

Not playable in Scrabble US: DEOXIDISE.