While Prince Charles and Lady Diana were leaving Buckingham Palace for their royal honeymoon yesterday, there was a gathering at Claude McKee's country place north of Upper Marlboro to celebrate a tradition much older than the House of Windsor -- Maryland Tobacco.

The No. 1 crop in Maryland as far back as the 17th century, tobacco now accounts for a Lilliputian amount of the state's total agricultural output. The fact notwithstanding, more than 600 persons came in Ford pickups, in dungarees and in caps advertising pesticides to the 31st annual Tobacco Field Day, sponsored by the University of Maryland, to see new equipment, to learn about new research in the industry and to socialize.

George Reeves, a St. Mary's County farmer, came because, "you get the benefit of research work that's done on improving Maryland tobacco. We also come to see the changes in tobacco equipment. Of course, tobacco is a labor-intensive crop, and we're always interested in ways of reducing labor."

To capitalize on that desire, Ed Starzec, a sales representative from a company in Ephrata, Pa., was on hand to display the newest thing in tabacco technology -- a $4,300 tobacco harvester.

"Until now, harvesting was done by hand," said Starzec, who's been displaying the harvester at different field days and dealer demonstrations from Pennsylvania to North Carolina.

Other equipment on display and demonstrated yesterday included tobacco sprayers, saw rigs, lawn mowers and tobacco planters.

This time of year the tobacco plants planted in March stand about 3 feet tall. When a pink blossom develops on top of the plant, it is broken off in a process called topping, because it is believed to improve the quality and yield of the leafy plant. Two weeks later, in August, the tobacco is harvested. then, it is sorted, graded and tied in "hands" for sale. t

The dollar value of all the Maryland tobacco sold during the auction season this spring was over $43 million, representing a $9 million increase over the previous year.

Roughly 22,000 acres of tobacco are grown on 4,000 farms in southern Maryland. Five or six acres is the average number of acres cultivated by most farmers. Maryland tobacco plants usually are speared on tier poles, or sticks, and air-cured rather than flue-cured. That is, it hangs in a curing barn for a month to 45 days and dries naturally instead of being dried by hot air passed through flues.

Claude McKee, an extension tobacco specialist who hosted the field day on the 200-acre university research farm, believes that the air-curing process and the limited use of nitrogen fertilizers may partially explain why Maryland tobacco contains an average of 2 percent alcoloids (nicotine and tar), as compared with 6 percent for tobacco grown in the Carolinas. Another reason for the low-nicotine content may be the sandy, loamy soil of the five counties located in the Atlantic coastal plain, which once was sea bottom.

McKee also extimated that approximately one-third of Maryland tobacco is sold to Swiss and German buyers. Swiss cigarettes are blended with as much as 9 percent Maryland tobacco, compared to American cigarettes that usually contain about one percent. European manufacturers prefer the Maryland tobacco that burns slowly, evenly and has a low nicotine content.

The tobacco industry, once the king of Maryland agriculture, no longer holds the appeal to young people that it did for generations of farmers like Earl Harper of Calvert County.

Young people don't seem to have the will or the patience to work hard for the relatively small profit and the infrequent payday. "The average young person can't wait a year to get their money," he said.