'Tis the safety season for parents picking tots' toys from a new lineup of products

The Smurf Musical Crib Train looks playful, not dangerous. But early this year one American child gagged on a piece of the yellow-and-blue toy. A worried mother reported the incident to the Consumer Product Safety Commission - and 4, 300 Crib Trains were yanked off store shelves.

This weekend, after the turkey and the football games, millions of parents will descend on crowded malls to begin their holiday shopping. United States officials are urging them to keep safety in mind when picking toys for tots.

Some 150,000 playthings are currently available in this country, ranging from blocks that would have been at home in the 18th century, to toy cars that snap apart and form robots. Three to four thousand new toys hit the market every year.

''We don't have the opportunity to pre-test everything that comes into the marketplace,'' says Nancy Steorts, chairman of the Consumer Product Safety Commission (CPSC). So parents should follow some basic guidelines when shopping, says Ms. Steorts:

* Pay attention to age labeling. Toys meant for children age three and above are not only more sophisticated, they often contain small parts that shouldn't go in small mouths.

* Check for sturdy seams on stuffed animals. Make sure eyes, ears, buttons, etc. . . are well-attached, and can't be ripped off and swallowed.

* Make sure rattles, squeeze toys, and teething rings are relatively large - again, so they can't be swallowed. ''A good rule of thumb is that if the base is smaller than the child's fist, don't buy it,'' says CPSC commissioner Terrence Scanlon.

* Projectile toys - arrows, darts, missiles - should have blunt tips, securely fastened.

* Toy chests should have sturdy lid supports, so the top won't slam down on a child's head. The Toy Manufacturers of America association this year adopted a standard calling for such supports.

The CPSC believes that toy-related injuries in the United States are on the decrease. There were 132,000 such injuries in 1982, estimates the agency, as compared with 118,000 for 1983.

Many of these injuries were caused not by any intrinsic quality of the toy, but by children falling off, hitting, or otherwise misusing their playthings, says the CPSC and the toy industry.

One of the sources of a number of serious accidents, for instance, is the common, everyday balloon. Small kids often can't resist stretching uninflated balloons, or pieces of popped ones, over their mouths. If they suck in too hard, the rubber can be accidentally swallowed. Two fatal balloon accidents have been reported to the CPSC this year.

''Keep uninflated balloons away from pre-schoolers,'' says Nancy Stoerts.

Crib gyms - colorful toys hung from a bar placed over cribs - are another common source of accidents. A child old enough to push up or crawl often grabs at the bar, and can get feet and arms entangled in the dangling toys.

''Crib gyms should be removed when kids are five months old,'' says Ms. Stoerts.

Four billion dollars worth of toys will be sold between Thanksgiving and Christmas. The Cabbage Patch Doll Award for the hottest selling item so far, goes to Hasbro's Transformers, say industry officials. The Transformers, priced from $3 to $30, are small robots that can be twisted and snapped into everyday objects, from cars to planes to tape recorders. Transformers are the stars of a weekly syndicated children's TV show - as are the Smurfs, blue troll-like dolls that are a constant favorite.

But in general, parents are turning away from glitz and high-tech and back to traditional toys, industry officials say.