The envelope was soft and as thick as summer cream. The stiff, formal card inside, embossed in gold with the royal seal, bore a brief but startling message: "The Lord Chamberlain is commanded by Her Majesty," read the elegant Florentine script, "to invite Mr. and Mrs. Tom Reid to a Garden Party."

And so it was that this gray and blustery afternoon found us--Peggy in her dashing new summer bonnet, me in my best dark suit--strolling the vast green park that serves as the back yard of Buckingham Palace. There we joined a few other guests--okay, there were 8,000 of us on hand--as Queen Elizabeth II hosted the first of this summer's royal tea parties.

The queen and her family have come in for intense criticism in recent years, but today at least, there was nothing to criticize. Her Majesty gives a marvelous party. The setting was dramatic. The savories, sweets and tea were delicious. The music was lively and eclectic--the military band even played Sousa's "Washington Post March," although I was probably the only one present who recognized it. Most of all, though, the various royals who attended were chatty and amiable in a surprisingly easygoing way.

For all the chamberlains, ladies-in-waiting and gentlemen-at-arms standing around in formal dress, the queen's party managed to be regal and relaxed at the same time. When a yeoman of the guard came over with his gleaming seven-foot spear to move the crowd clustering before the Royal Tea Tent, he flashed a friendly smile and said, "Come on, folks, can't you give us just a step or two backward now?"

At the urging of our British friends, we had spent some time in recent days swotting (that is, cramming) over the standard text of royal etiquette, "Debrett's Correct Form." It set forth a bewildering hodgepodge of do's and don'ts about introductions, titles, curtsies and bows ("The head only; not from the waist").

We had fun watching the lines of guests today stooping in consecutive curtsies--it looked like a baseball park wave played in reverse--as members of the royal family walked past. When I nudged my spouse and asked whether she would curtsy, she looked at me as if I had forgotten the Revolutionary War. "Not on your life," she hissed. "We don't have a queen."

On the ticklish subject of "addressing the sovereign," Debrett's was strict: " 'Your majesty' for the first time. Subsequently 'Ma'am.' This should always rhyme with Pam. Pronunciation to rhyme with Palm has not been correct for some generations."

In fact, when the smiling queen came by, wearing a knee-length silk dress of (what else?) royal blue and a matching broad-brimmed hat, none of this rigamarole seemed necessary.

The guests formed two long lines that snaked for about 100 yards across the grounds. Her majesty strolled down the middle, now and then stopping to shake a hand and engage in a chat. Sometimes she greeted people she obviously knew; mainly, though, she just picked people out of the crowd, stuck out her gloved hand and said, "Good afternoon."

Her husband, Philip, the Duke of Edinburgh, and her oldest son, Charles, the Prince of Wales, seemed even more approachable. Philip was particularly drawn to guests in uniform, whether it was teenage seamen from the HMS Excellent or aging veterans proudly wearing their regimental blazers or corps of women in the Robin Hood-style forest-green suits of the Royal Volunteer Service.

The guest list, drawn from every element of Britain's increasingly varied population, is probably the most striking aspect of the queen's party-giving style. When Queen Victoria started these summer tea parties behind the lavish neoclassical palace in the 1860s, her guests tended to be crowned heads, dukes and diplomats. But Britain has become a much more democratic nation, and the monarchy has changed with it.

At the three garden parties Elizabeth II holds here each July, most of the guests are untitled citizens working in government, charities and service industries.

At today's event, the Royal Tea Tent--actually an extravagant green-and-white gazebo beside the palace lake--was the smallest structure on the grounds. The Diplomatic Tea Tent was slightly larger, but the largest gathering spot was the place tactfully designated the Main Tea Tent--although most of the guests we met called it "the commoners' tent."

Since we are commoners--from a former colony at that--our friends here wondered aloud how we got invited to the royal do. Three theories emerged.

One idea--appealing, but unlikely--is that Peggy and I are so suave that no palace party would be complete without us.

Others suggested that the lord chamberlain's invitation was the palace's way of saying "no hard feelings." Earlier this year I wrote a column criticizing the queen's grammar. This became a mini cause celebre in the British media. Some papers agreed with me; others insisted, as the Observer put it, that "Americans should not interfere with what we know best." Perhaps, then, we were asked to the party to show that the palace holds no grudge.

Or it may just be that a few foreign journalists are asked to join the fun each summer, and my name was pulled out of the top hat. That's the least exciting theory, but the most plausible.

Whatever, it didn't seem to matter at all today. When Philip, with his walking stick in one hand and his gray top hat in the other, stepped over in my direction--I was standing with a clutch of army officers--he said, "We're so happy you could join us." And on a thoroughly congenial afternoon at the palace, it was easy to believe that he meant it.