Tomorrow is the big sporting event of the year in Pennsylvania. Forget the World Series, the Super Bowl, the Stanley Cup, the NBA playoffs. Tomorrow is Opening Day - the first day of the main two-week period when it is legal to hunt deer with a firearm. Though Guinness has not weighed in on the matter, Opening Day in Pennsylvania is arguably the largest single participatory recreational event in the world.

The state Game Commission estimates that 750,000 men, women, and children will be spread over a legal hunting area big enough to swallow New Jersey. Before the season ends Dec. 12, about 900,000 hunters clad in safety orange will spend at least a few hours in the fields and forests. That's more than the combined number of active-duty personnel in the Army and Marine Corps.

It all begins, officially, one half hour before sunrise (6:32 a.m. in eastern Pennsylvania, 6:52 a.m. in the west). If things go as expected, one in every three hunters will succeed. Of the 300,000 deer that are killed over two weeks, about a third will die before the smoke clears tomorrow - and most of these will die before 9 a.m. The deer aren't aware that the season begins tomorrow, but they learn fast.

Indeed, Odocoileus virginianus, the white-tailed deer, is a marvel of grace and speed that is a worthy adversary for the honest sportsman. Deer have extraordinary sight and hearing, and their sense of smell is so keen that they can detect an acorn under two feet of snow. They are superathletes that can sprint 100 yards in five seconds in 20-foot bounds and easily jump an eight-foot fence.

Opening Day is the state's unofficial holiday. Pennsylvania has more deer hunters than any other state. Many public schools in rural Pennsylvania will be closed tomorrow, and those that aren't will experience heavy absenteeism.

Some labor contracts have clauses designating Opening Day a paid holiday. In the past, court trials have been postponed because key witnesses were off in the woods. There will be a general reduced availability of manpower everywhere. Buildings have burned slowly to the ground because all the volunteer firefighters were in the woods.

New Jersey's main firearm deer season runs Dec. 7 to 12. Licensed hunters are allowed to harvest two antlered deer. New this year is the legal use of a bow (recurve, compound, or crossbow) during the firearm season.

Among the Pennsylvania hunters planning to be in the woods tomorrow is 69-year-old Joe Kleiner of Souderton, who has been stalking deer since he was 16.

"It's something you just can't explain to someone who's never done it," said Kleiner, a retired landscaper. "I was raised on a farm, and it's a very deep part of me. You have to love nature. You have to love the outdoors. It's just magic."

Kleiner, who figures he's taken 40 deer in his half-century-plus of hunting, expects to be in a tree stand well before first light, near his cabin in rural Tioga County. He said his five adult children - four sons and a daughter - planned to be out for Opening Day in various parts of the state.

George Williams, a 68-year-old retired gas company employee from Collegeville, plans to be where he's been every Opening Day for about 50 years - in a tree stand atop Dutch Mountain in Wyoming County. Williams said he had begun hunting with his uncle when he was 12.

"I still get pumped up for Opening Day. Part of it is a feeling of communion with the deer. The whitetail is smart and wily and has a knack of picking up your scent. Once those first shots are fired, they know it's hunting season.

"I worry about their survival. When I was younger, I would harvest anything that was legal, but in recent years, as a conservation measure, I have taken only the most mature deer and let the younger ones go."

The pop-pop of gunfire isn't the only frequent sound on Opening Day. There's also the ka-ching of cash registers and the brrrrppp of credit-card scanners. Hunting is big business in Pennsylvania, pumping $1.6 billion a year into the state's economy, according to the U.S. Fish and Wildlife Service.

This weekend the highways leading to Pennsylvania deer country have been jammed with all manner of vehicles carrying guns, ammunition, food and drink, and camping equipment.

Diners featured signs promising "Hunter's breakfast, 4 a.m." Meat processors hung out homemade signs: "Deer cut here." Motels booked for nearly a year were providing special racks for successful hunters to hang their carcasses.

The deer hunt is a cultural ritual throughout rural Pennsylvania. In Pennsylvania: A History of the Commonwealth, edited by Randall M. Miller and William A. Pencak, it is described: "Hunters extol their union with nature, initiate novices and recognize seasoned veterans, engage in long rounds of storytelling at primitive lodges, and don earthy dress and body appearance to separate the activity from modern life. In their talk, they often speak of the days of yore in the primitive wilderness and imagine themselves as part of a classic American story of triumphing in the woods."

The enduring icon of the deer hunt is the deer camp.

"Camp may be a cabin you own and invite some friends or family to share, a rental unit, or an organizationally held structure, for which you pay dues for maintenance," writes Pennsylvania State University folklorist Simon Bronner. "Camp is the common destination, because going hunting usually involves taking a 'hunting trip' away from home rather than hunting at home. . . . The 'traditional' camp is not comparable to a 'second home,' because more than likely it will lack modern conveniences of indoor plumbing and electricity. Heat will probably be supplied by a stove or fireplace, light and cooking with propane gas."

But the deer hunt isn't quite what it used to be. There are 926,000 licensed hunters in Pennsylvania, a decline of about 13 percent from 10 years ago.

The precise size of Pennsylvania's deer population is a matter of hot dispute. Hunters say there are too few. But farmers, foresters, and some suburbanites say there are too many.

The Game Commission stopped counting the statewide herd about eight years ago because it believed there was no point. The last estimate was 1.5 million deer in Penn's Woods.

However, the commission will say that when the final round is fired on the final day of deer season, about 300,000 fewer deer will be roaming in Pennsylvania.

Home is the hunter, home from the hill, with his deer or his alibi.