Nevertheless, pairing Wilson and Vaughn strengthens the weaker moments and makes the better ones explode with comic energy. "Wedding Crashers" is enough of a laugh-getter that New Line can anticipate a boxoffice hit.

Wilson and Vaughn play John and Jeremy, a couple of guys making a living in Washington, D.C., as divorce mediators -- this gets established in a funny opening scene -- but that's not their real claim to fame. No, what makes them very special guys is this great girl-catching gimmick they have developed: They crash weddings. Weddings, you see, bring out a lot of hot women, the ceremonies get them all romantic and the parties lessen their inhibitions. As long as the two have a well-rehearsed explanation as to who they are and how they are related to the bride or groom, the game is almost too easy.

Then the inevitable -- read predictable -- happens: One of the guys breaks the rules of the game by falling in love. This happens when they crash the wedding of the daughter of Treasury Secretary William Cleary (Christopher Walken) and hit on bridesmaids Claire (Rachel McAdams) and Gloria (Isla Fisher) Cleary. Each spells trouble.

For John, Claire presents a double challenge. He not only falls for her but also is blocked by an obstacle in the form of her highly competitive boyfriend, Sack (Bradley Cooper), scion of another East Coast political clan. For Jeremy, Gloria turns out to be a "clinger." After a satisfying tryst on the beach, Gloria refuses to leave her new love's side. She even gets her father to invite the boys back to the family compound for an exclusive post-wedding party.

Jeremy wants to flee fast, but John clearly needs more time with Claire to win her over -- a whole lot more time. So John insists that Jeremy must tarry and back him up. Soon their cover stories are looking shaky.

The central feature of the midsection of the movie are the eccentricities of the Cleary clan, who are Kennedy-esque only much naughtier. The secretary is a self-centered philanderer; his wife, Kathleen (Jane Seymour), a lush on the make for younger men like John; Gloria, a virtual nymphomaniac; and brother Todd (Keir O'Donnell), a bad artist and, as Grandma Cleary so inelegantly puts it, "a homo."

Then a funny thing happens to this comedy with an edge of political satire: It takes a detour into SitcomLand. Characters turn into caricatures, and soon the family is more crackpot than eccentric. None is capable of getting appointed rat catcher much less Secretary of the Treasury.

It's a loss but a minor one as the film still has merry fun with Wilson and Vaughn cutting loose in this loony household. And McAdams and Fisher are more than just good-looking actresses; each has a solid knack for comedy. Walken always makes more of such roles than is really there, but much more should have been done with Seymour's character.

Director David Dobkin ("Shanghai Knights") moves the two-hour comedy quickly enough so few viewers will dwell on plot holes or character deficiencies. The technical side is bright, especially a montage by editor Mark Livolsi of the boys working their amorous magic at a series of Jewish, Irish and Italian weddings. Julio Macat's cinematography is sharp, and Barry Robison's sets and Denise Wingate's costumes portray a class of people exceedingly comfortable with their undeserved riches.

Audiences are probably expecting Wedding Crashers to be a showcase for Vince Vaughn's rantings and Owen Wilson's standard but affable chum act — and it is.

Plotting their next move: Owen Wilson, left, and Vince Vaughn are two buddies on the make in Wedding Crashers.
New Line Productions

But you can thank the family of oddballs led by Christopher Walken for bolstering the film's middle hour — probably the reason this spotty farce has been enjoying advance buzz of above-average decibel count. And this is in a movie year when sustained laughs have been few.

Think of all the loopy eccentrics Walken has played, and then look at the clan his character in Wedding Crashers has sired. The tally: Just about the number of jokers you'd expect to get from shuffling the deck of the actor's screen gene pool.

After a funny opening scene that establishes the two leads as divorce mediators, we come to understand the significance of the title. Just as a character in Mike Nichols' underrated and funnier What Planet Are You From? (2000) hung out at Alcoholics Anonymous meetings to pick up women, Vaughn and Wilson do so at weddings. And for the same reason: Their targets are at their most vulnerable.

Masters of identity duplicity at receptions, the two dance their way into bridesmaid sexcapades in one of the year's randier screen montages before hitting the wall. The daughter of Treasury Secretary Walken is getting married, and she has two sisters. The one played by The Notebook's Rachel McAdams melts Wilson's heart, and thus a philandering scheme is foiled.

The movie hits its peak when the two buds get invited to the family's summer home. Another sister (Isla Fisher, stealing the show as a presumed innocent) hooks up with clueless Vaughn and, in the movie's most discussion-inducing scene, gives him a protracted crotch massage under a packed dinner table. A weird brother (Keir O'Donnell, ripe for the mad hunchback role in a Frankenstein remake) hits on Vaughn as well. And mom Jane Seymour (looking as if she swallowed a Dr. Quinn youth potion) beckons Wilson to feel her new breasts, and, well, who wants to be a rude guest?

These R-rated rompings are absolutely welcome and may be enough to ensure a midsize hit. But Crashers slumps badly in the stretch when the filmmakers have to find a way to surprise us when we're fully aware of where the story is going. The solution is to bring on a surprise cameo by the screen's most currently overexposed actor. He crashes the movie, and the subplot he brings with him saps its strength, though it doesn't kill a premise that could have delivered even more.