The spirit of Christmas still hangs heavy over our house, entangled in ribbons of model railroad track.

I hadn't realized how much had been missing from recent Christmases until a neighbor suggested we take his family's HO gauge set on indefinite loan, since their toy of the season was a new home computer. As we amalgamated their set with fragments from our old one, memories of yesteryear came flooding back, borne on the old familiar cries:

"It's my turn!"

"You're running it backwards!"

"I told you to throw the switch, dummy!"

"Now you've broken it!"

"This is a stupid layout!"

"I liked the town the way it was!"

"I'm going to tell Dad!"

In truth there isn't much to tell Dad, because he does most of the yelling. My grasp on adulthood is tenuous at best, and is fair swept away by the buzz and whine and click of toy trains.

Especially HO gauge trains. I had a Lionel set as a boy, but never could fully suspend my disbelief because of the three-rail track. I might have adjusted had it not been for Johnny Cavanaugh, who lived across the street.

Johnny, or more precisely his father, had a fabulous HO system that filled most of the basement. His mother had to make do with a tiny laundry corner, and anything that was stored downcellar was as good as lost, because it disappeared under the waist-level platform that carried the tracks from coal bin to furnace to water heater and back, piercing whatever walls were in the way.

It was awe-inspiring to watch Mr. Cavanaugh run the trains. The ethics of model- railroading forbade him and his train-nut friends to lay a finger on the layout once it was declared operational for the evening. Everything was done from the command panel, which was a fair approximation of a power-station control room. Trains were formed up by yard engines and remote- control switches and dispatched by stopwatch according to rigid timetables. One after another, the strings of cars would disappear over trestles and through tunnels into adjoining rooms. A crack passenger train might be sharing a main line with a lumbering freight, but no matter: At the appointed time, a button would be pushed and the freight would be shunted onto a siding as the 20th Century Limited or the Super Chief highballed past.

The men would work as many as half a dozen trains at a time, and occasionally something would go wrong, but it was still hands-off. If special repair trains couldn't clear the track, that part of the layout was shut down for the evening.

We boys were absolutely forbidden to touch the layout, so of course we raced home from school to play with the trains (the long-suffering Mrs. Cavanaugh being careful not to notice; she always clumped around to warn us she was coming downstairs). It was necessary to remember exactly where everything was -- Mr. Cavanaugh always did -- and leave it just so. I assumed the penalty for getting caught would be death, but it turned out to be worse: permanent exile.

I never got over it, and since Christmas have been trying to reproduce Mr. Cavanaugh's vast layout on a single sheet of 4 x 8 plywood. Track circles and crosses track, trestles rise and twist and dip; one peters out in thin air, there being no place for it to come down. Everything's crammed in so tight only short trains can be run without derailing, which is just as well, since long trains would butt their own cabooses.

There are five engines, three trolleys and 26 cars, and the crashes are most satisfying. When the sun comes up I close the curtains so as not to lose the effect of the headlights.

Now and then the children come whimpering round to ask when it's going to be their turn to play. I tell them to grow up and pick on their own kids.