A certain shift in demeanor of the Muzak at the Safeway, and a steadily growing increase in the thickness of The New Yorker, signal the onslaught of the holiday season. To make it official, television is brimming excessively with seasonal specials, and it is very unlikely that any of them will equal in charm a fit of innocence from public TV titled, "Christmas Eve on Sesame Street."

The special will be seen Sunday night at 8 on Channel 26 (which may delay it slightly for more oppressive fund-raising) and other public TV stations, then repeated on Channel 26 Thursday, Dec. 21 at 8 p.m. and Saturday, Dec. 23 at 11 a.m. Many PBS stations will also show it Christmas Eve at 7 p.m.

In addition, CBS has its own Sesame Street holiday special set for next Friday, but a spokesman for the Children's Television Workshop, creators of "Sesame Street," says that special was produced not by CTW but by Bob Banner Associates, which merely rented the rights to use three Muppet characters: Oscar the Grouch, Big Bird and a new dog named Barkley.

Grouch and Bird join Kermit the Frog, Ernie and Bert, The Cookie Monster, Mr. Snuffleupagus and some essentially negligible human beings on the public TV special, which opens with a sweetheart of an ice-skating sequence involving the great yello-feathered fowl and an agile little girl. Oscar the Grouch takes a great fall in his garbage can and retaliates by vexing one and all with the philosophical question, "How can big fat Santy Claus get down all those skinny little chimneys?"

The hour includes a nimbly adapted version of O. Henry's "Gift of the Magi," as interpreted by Ernie and Bert, such revered musical chestnuts as "Have Yourself a Merry Little Christmas," and original musical material by David Axelrod and the late Sam Pottle. There is not merely one happy ending but a whole series of happy endings along the fabled Rue Sesame, that most blessedly unreal of all manufactured TV neighborhoods.

The air is brisk with racial harmony, choral harmony. contagious cheer, peace on earth and good will toward Muppets. The special, produced and directed by Jon Stone, finds Jim Henson's inspired creations and the CTW staff excelling at what, for 10 years of "Sesame Street," they have always done well -- tugging at the heart instead of the sleeve.