Connoisseurs of fast food and human behavior were doubly satiated today as anxious crowds of Soviet customers engaged in traditional pushing and shoving to place ''Beeg Mek'' orders at the nation's first McDonald's restaurant, only to be calmed by uniformed compatriots dictating that they have a nice day.

''We added our own spice to the menu, our usual commotion,'' said Valentin Gmyzin, a pipe factory worker, after making it through the counter crush at 27 cash registers and spending four days' salary for a Big Mac, cheeseburger, apple pie and two milkshakes.

As exotic as the food seemed, opening-day customers said they were most impressed at the simple sight of polite shop workers - Soviet workers - somehow having been trained in this nation of commercial boorishness to actually smile and say, ''May I help you?'' and ''Thank you for coming.''

''There is a lesson to be drawn from this for the country,'' said Tatyana Podlesnaya, a teacher. ''What is killing us is that the average worker does not know how to work and so does not want to. Our enthusiasm has disappeared. But here my meal turned out to be just a supplement to the sincere smiles of the workers.''