It's still hard to realize that this will be our first Christmas without Bing Crosby and our first New Year's Eve without Guy Lombardo.

But through the eerie reassurance of videotape, Crosby returns tonight for one last celebration, a CBS special called "Bing Crosby's Merrie Olde Christmas," taped five weeks before his death and airing at 9 o'clock on Channel 9.

Clearly this is a viewing occasion when all normal standards may be dropped and sentimentality allowed to flow like eggnog. In fact, however, this special would be a heartwarmer regardless, having been beautifully produced in London by Gary Smith and Dwight Hemion and directed by Hemion so as to seem as comfortable as a Sunday afternoon nap.

Words and songs by Crosby that wouldn't otherwise be unusual do take on added meaning, of course. He ends the show, naturally, singing "White Christmas," but just before that he calls the holidays "a time to look backward with gratitude at being able to come this far, and a time to look ahead with hope and optimism."

And then he says, "Till next time . . ."

The program features, as is the annual custom, Bing's family, who sing less this year than in the past and are therefore much easier to take, plus actor Ron Moody, Twiggy, and music hall star Stanley Baxter, who does the funniest imitation ever done of Crosby's pal Bob Hope.

But the most distinctive guest, in the best and worst senses, is rock star David Bowie, whose gaudily decadent public persona would seem utterly inharmonious with the dean of steady-as-she-goes.

"I'm Bing," Crosby says, shaking Bowie's hand. They not only get along, they make agreeable music together. A later Bowie solo is definitely on the discordant side, but it's strikingly shot and gratifyingly brief. Crosby looks gallantly unfazed by it, as he always did by everything - even including himself.

With Twiggy he sings "Have Yourself a Merry Little Christmas," which is a tearjerker under almost any circumstances, and which here becomes awesomely poignant on the line, "Through the years, we all will be together, if the fates allow."

We really did think - didn't we? - that Crosby would go on through all our Christmases. It was part of the merriness and the brightness, and it attested to the amazing familiarity bred by radio and especially by television. Bing was a member of millions of families he never even saw, and tonight television will bring him into their homes again.

It is hard to think harshly of an instrument that can do that.