If you want to send photo holiday cards this year, now is the time to not only start thinking about them, but to do something. The deadlines are fast approaching to personalize your holiday greetings with photographs of your children, house, cat or sailboat.

Assuming you're taking your own pictures, here's a sampling of photo labs that will print cards from a customer's negative, print or slide:

* Berkey Film Processing (Alexandria, Va., orders available at Giant Food Stores) -- Deadline Dec. 7. Color photos only on flat card, 3 1/2 x 5, choice of messages, including "Happy Chanuka." Prices: 20 for $9.59, 40 for $17.99, 60 for $25.79, 100 for $39.95. $3.95 extra for cards made from slides and prints.

* Colorfax Labs (21 stores in the area) -- Deadline Dec. 21. Color "slim line" (3 1/2 x 7): 25 for $17.75, 50 for $34.50, 100 for $66, 200 for $128; "trim line" (3 1/2 x 5): 25 for $15.50, 50 for $29.50, 100 for $57, 200 for $110. Will print black and white for extra $5.25 charge.

* District Photo (part of Clark Color Labs in Beltsville) -- Deadline Dec. 10 for picture from a negative. "Slim line" prices: 25 for $10.25, 50 for $19.50, 75 for $28.75, 100 for $38. A charge of $3 extra if print made from another print or slide. Black and white printed on colored paper also available. (Among places orders available: People's Drug Stores, Dart Drug Stores, Safeway Stores and Snapshot Stores.)

* Fotomat Labs (57 locations in D.C., Md. and Va.) -- Deadline Dec. 8. Flat 4 x 8 card. Photos printed only in color. Prices: 10 envelopes and cards, $2.95; for additional cards just multiply. A $2.19 extra charge for pictures made from slides or prints.

* Kodak -- Deadline Dec. 3. Only cards in color. Suggested prices same as Colorfax.

* Photronic Labs in Beltsville (orders available at Ritz Camera Stores) -- Deadline Dec. 1. Printed card 5 1/2 x 7 1/8 with space for picture inside message. Photos only in color: 12 cards and prints, $8, 25 for $14, 50 for $27, 75 for $40, 100 for $50.