AT the moment he had been waiting for all his life, Peter Sommo fell to his knees in front of the television set, held his head in his hands and shouted a quick prayer of thanksgiving. And every so often later that Sunday in 1982 as he hurried about the Knickerbocker Country Club, where he has been a waiter for more than a decade, he suddenly shed a tear and suddenly sang a song under his breath, occasionally at the same time.

''Is there anything,'' somebody asked, ''the matter with Peter?''

''He's just celebrating,'' another said. ''Italy won the World Cup.''

That's what the World Cup means to thousands, if not millions, of Americans who wonder why other Americans don't appreciate soccer as much as they do. And now 48-year-old Peter Sommo, once a steward on the Italian ocean liner Raffaello Michelangelo after having grown up near Genoa, is celebrating again. This time because the United States has been designated as the 1994 host of the World Cup tournament.

''When the announcement was scheduled for July 4, I assumed the United States would get it, but you never know,'' he said. ''Monday morning, I woke up about 5 o'clock. I turned on the radio, but it wasn't until a quarter to eight that the news finally came over.''