EXCLUSIVE

Fred Willard was arrested for lewd conduct last night in Hollywood when police allegedly caught him with his pants down in an adult movie theater ... TMZ has learned.

According to law enforcement sources, LAPD undercover vice officers went into the Tiki Theater in Hollywood and found the 78-year-old "Anchorman" star watching last night's feature ... with his penis exposed and in his hand.

We're told Willard was arrested around 8:45PM and booked for lewd conduct.

It was a quick release -- we're told he was out of police custody a short while later.

As for which movie Fred was watching -- there are 3 flicks in rotation at the theater ... "Follow Me 2," a XXX parody of "The Client List," and "Step Dad No. 2."

Willard is best known for his memorable roles in "Best in Show", "For Your Consideration", "American Wedding" and "Everybody Loves Raymond." Willard is best known for his memorable roles in "Best in Show", "For Your Consideration", "American Wedding" and "Everybody Loves Raymond."

According to IMDB, Fred is "rumored" to be in pre-production for a movie entitled ... "The Yank."

It's a comedy.

8:47 AM PT -- We're starting to get comments from people who say Fred is 72 and not 78 ... but official records show that he was born on September 18, 1933 ... NOT 1939.



7:06 AM PT -- Law enforcement sources tell TMZ ... the LAPD vice officers were not conducting a raid ... but rather a "random walk-through" of the premises.

We're told ... when theaters like this get their license, they have to allow cops in whenever they want ... to inspect.

In fact, the theater has a sign posted in the front which warns customers that the theater is "viewed by LAPD."

The theater also warns, "No Alcohol, No Weapons, No smoking inside" ... and no pets.