Pay attention to the dates on food products not only when you buy, but also in your cupboard, remembering to rotate them and use the oldest first. Supermarkets don't always rotate their products, and spotting an outdated sell-by date is not uncommon. Bring it to the attention of the store manager.

If you have a question regarding the dating on a particular product, you can call the manufacturer. Several list toll-free numbers on the side of the package for just that purpose.

Additionally, the following sources on open dating are available:

* The April-May 1984 "Thumbs Up" guide published by Giant Food lists recommended storage times and handling hints for more than 300 products. For a copy, call 341-4365 or write Giant Food Inc. Consumer Affairs, P.O. Box 1804, Washington, D.C. 20013.

* The Montgomery County Office of Consumer Affairs published a booklet ("Crack the Codes: A Guide to Understanding the Codes on the Foods You Buy") that unraveled the coded dating and shelf lives of numerous products. It is being updated and should be completed by May. The office will not accept advance orders.

* The "Safe Food Book: Your Kitchen Guide," published by the U.S. Department of Agriculture, details shelf lives, storage tips and product safety. Clip and save this: although the guides are out of stock, they are in the process of being reprinted and should be available by the end of February. For a free copy, write Consumer Information Center, Pueblo, Colo. 81009. Ask for Home and Garden Bulletin No. 241.

* USDA also publishes a booklet called "Your Money's Worth in Foods" that deals more with money-savings tips, but which also talks about open dating, storage and handling. For a copy, send a $2.25 check or money order payable to Superintendent of Documents, U.S. Government Printing Office, Washington D.C. 20402, or call 783-3238. The 40-page booklet is Home and Garden Bulletin No. 183.