There are parties, and there are parties. But The Party of the hundreds of inaugural receptions, lunches, dinners, breakfasts, balls, galas and parade watches is tonight. How can you tell it's the ultimate? When a guest list starts with Frank Sinatra, what other clue do you need?

There will be about 50 guests at the Italian Embassy tonight for the dinner-dance Ambassador Rinaldo Petrignani and his wife Anne Merete are giving in honor of their California friends, better known in some circles as the Reagan "kitchen cabinet." But it is Sinatra who counts.

"I've got one shot of six in sitting with Frank Sinatra," says one of the chosen who will be there tonight.

Consider the responsibility of being Sinatra's host.

A few invitations went out to the media last week. Sinatra, not known to be a media groupie, arrived in town on Sunday. Monday morning, at least one reporter was disinvited by an Italian Embassy spokesman, his voice heavy with embarrassment. The reason given was that the hostess was forced to go out of town for "personal matters," and might not be back in time for the party. The spokesman said that because of this, the ambassador decided to make the party a private dinner.

"Therefore, there will be no press coverage of any kind," the spokesman said.

Consider the plight of a hostess giving another party on the same night as The Party.

There is word that at least one hostess wanted to change the date of her party when she heard of the Italians' dinner, knowing it would pick off the cream of her guest list. But her guest of honor balked. His schedule couldn't be changed.

Consider the position of those who don't need to worry about such things.

White House Deputy Chief of Staff Michael K. Deaver is throwing a birthday party for his wife Carolyn tonight. They were invited to the Petrignani party but you didn't find them trying to reschedule their dinner. In fact, their party will be the first function to be held in what shows every sign of becoming the new "in" watering hole: Glorious Foods Cafe in Georgetown.

Consider the prestige of being Glorious Foods this inaugural week.

In addition to tonight's party, Friday's luncheon, hosted by USIA director Charles Z. Wick and his wife Mary Jane, an inaugural committee special consultant, and Attorney General William French Smith and his wife Jean, will be at Glorious Foods. Their guests will be the same glorious group who get together tonight at the Italian Embassy. Glorious Foods caterers will also prepare the inaugural lunch for President Reagan and the Congress in Statuary Hall following his swearing-in on Monday.

All weekend, this same, select group will be running into itself again and again, but its members are not the only ones who will be caught up in the tornado of inaugural parties that began this week.

If you're from Florida, you can attend a breakfast with Jeane Kirkpatrick, a steak dinner with your chums from home, a state Republican breakfast, a Super Bowl party and a special Florida inaugural ball. This list does not, of course, include any of the official inaugural functions.

Every taste and special interest group is represented. There are out-of-towner parties for everyone from an entire state and in-towner parties for everyone from a certain block in Georgetown. Corporate parties where CEOs can preen and polish the image of products ranging from Nutrasweet to automobiles to Time Inc. Fund-raising parties for just about every conservative group you've ever heard of. Parties for young people, for old people, for black people, for Hispanic people, for athletic people, for volunteering people, for handicapped people, for heroic people and for "good people from the state of Texas." Balls and balls and more balls, both inaugural and "counter inaugural."

Shell Oil has shipped in chef Paul Prudhomme to add a Cajun touch to a pre-inaugural ball party at the Corcoran. Charlton Heston will give a patriotic reading and Arnold Schwarzenegger will be Arnold Schwarzenegger at a dinner for the American Security Council Foundation, a "pro-defense" group. Lew Lehrman and his Citizens for America will host three, count them, three parties for people like Jeane Kirkpatrick, Edwin Meese and Faith Whittlesey.

There are fewer black-tie events than last time and no white-tie, but don't be fooled. These are not casual pizza-and-beer gatherings. The food being ordered, according to Jose' Valado, senior vice president at Ridgewell's caterers, is "sophisticated, creative. It's very ornate, very decorative."

So watch for American flags fashioned out of fruit and herd after herd of chocolate elephants. And watch for the Reagans. Chocolate elephants can carry a party only so far. If you see the First Party Couple at your event, even if they're not there long enough to nibble at the flag, you'll know you've reached party heaven.

Some highlights:

* The Coors Party -- 250 people will board the docked "First Lady" tomorrow night and join Reagan kitchen cabinetman Joe Coors for a "Monte Carlo night" to benefit Paul Weyrich's Free Congress Foundation. "We tried to limit it," says publicist Sally Reed, "to make it as small and as exclusive as we could." The tickets cost $1,000, but guests get something back -- $50,000 in complimentary chips to use at the blackjack, craps and roulette tables. There will also be an auction where those $50,000 in chips can get you a trip to Monte Carlo, Las Vegas or Atlantic City, or a lunch with Sen. William Armstrong (R-Colo.)

* The Athletes' Party -- A whole lot of sports stars will be at a Super Bowl party Sunday in honor of National Athletes for Reagan thrown by the Jefferson Educational Foundation, which cultivates young conservatives. Arnold Palmer, Richard Petty, Cathy Rigby, Larry Holmes, Joe Frazier, Yogi Berra, Willie Mays, Chris Evert, Joan Benoit and others will romp across the specially installed Astroturf at the Sheraton-Carlton. There will be, of course, a 12-foot TV screen for watching The Game, decorative goal posts at either end of the room, an "All-American buffet" at half time and a 100-member marching band from Utah. $100 per person.

* The NCPAC Party -- Perhaps NCPAC should leave the conservative-boosting field and just devote itself to throwing parties. First there was the must-attend barbecue at Nelson Bunker Hunt's ranch in Dallas during the Republican convention, then the Bob Hope-hosted election night bash, and now the laser/video/star-stocked gala at the Pavilion at the Old Post Office on Sunday. Sammy Davis Jr. will entertain and Ava Gabor, Lorne Greene, Scott Baio, Ken Norton, Lou Ferrigno, Esther Williams, Dick Van Patten, Paul Williams, Sen. Strom Thurmond (R-S.C.) and others paying $1,000 a head will be there to honor outgoing White House Chief of Staff James A. Baker. A conservative PAC honoring James Baker? Isn't that something of a surprise, you ask? "Yes and no," says NCPAC spokesman Brad Mont. "If you want to lump all conservative groups together, the answer is yes. But if you look at NCPAC's record with Jim Baker, the answer is no. NCPAC and Jim Baker have worked well together."

* The National Black Republican Council Party -- According to organizers, this gala on Saturday night marks the first time any black organization affiliated with the Republican Party has sponsored an inaugural event. "We had a need to be more visible and more upbeat," says Connie Mack Higgins, chairman of the event and local chairman of the D.C. National Black Republican Council, an official affiliate of the Republican National Committee. Upbeat means 100 people will be entertained by a "Vegas-type show" with Jeffrey Osborne and Joyce Kennedy, the duo who recorded "The Last Time I Made Love." "It's us preparing for the 21st century," says Higgins. "Not only does the show represent a new thrust in the black Republican image, but also the involvement of so many young black Republicans." The Counter Inaugural parties -- When you call for information about the Alternative Inaugural Ball at the Kilimanjaro, the answering machine also tells you how to volunteer for the National Nuclear Weapons Freeze Campaign. Sponsors of the event include NOW president Judy Goldsmith, George McGovern and Rep. Patricia Schroeder (D-Colo.) and the guests will pay a mere $5 each to attend.

* Then there's the Americans for Democratic Action party at the Wax Museum, where there will be 500 people, some Redskins, jugglers, "All-American chili" and, according to spokeswoman Judy Newman, "lots of flags and bunting because Democrats like flags and bunting, too."