In Chester County in the summer of 1957, Steve McQueen was insufferable.

"He was an absolute horror," producer Jack Harris said yesterday, "but I loved everything he did for us."

That was the summer that Harris gave the 27-year-old McQueen his first starring role, in the sci-fi classic The Blob.

For the 50th anniversary of the film's shooting in Chester County, the producer - a 1936 graduate of Central High in Philadelphia and now 88 - returned from Beverly Hills, Calif., for the first time since that horrible summer.

For more than nostalgia.

In Phoenixville, the river town an hour's drive from Center City, it was the eighth annual Blobfest, a celebration of the movie and the legends.

The two-day event, which ended yesterday, is produced by the Colonial Theatre, the movie house where, in the film, the Blob begins its fiendish escapade of death and destruction.

Haven't seen the film?

The Blob is an alien life-form deposited in Chester County by a meteorite. It grows larger and redder as it devours all in its path.

Sort of like a repo crew towing away cars whose payments are so late.

What stops the unkillable glob is a bunch of folks wielding fire extinguishers, the foam from which freezes the beast so that it can be transported to colder climes.

No Academy Award. No Pulitzer. No Nobel.

"Just fun," said June Breit, 56, a registered nurse from nearby Audubon who had encased herself in red iridescent fabric to resemble - you got it! - the Blob.

"Can't beat fun in your backyard," Breit said.

That's why she - a crowd favorite in the costume competition - was suffering in the harsh glare of noonday sun, in the blocked-off street in front of the movie house.

On Friday night, more than 1,000 folks had entered the theater. And then, screaming like the film extras who were trying to escape from the Blob as it snacked on tasty theatergoers, they stampeded onto Bridge Street.

Yesterday, The Blob - slow, our racing hearts - was shown three times.

Mary Foote, 48, executive director of the private nonprofit agency that reopened the 1903 movie house in 1999, said she had started Blobfest "as a way of promoting the Colonial."

A Manhattan newspaper item about Blobfest had attracted Julie Stine, 45, her husband and their infant.

"I don't generally venture this far west," Stine said of the two-hour drive from their home in Hunterdon County.

Looking around at the costumed folks threading through the street party, she said, "I like the quirkiness."

In an interview at a restaurant across from the Colonial before he was to speak at a panel discussion, Harris said this, the first film on which he was the producer, cost only $130,000.

The U.S. Bureau of Labor Statistics says that's equivalent to $962,041 today - a definition of low-budget film.

It has earned - cue the applause sign - $4 million.

So what was the problem with McQueen?

"At breaks in the shooting," Harris said, "he would take his little MG and go over those [tight] roads in Valley Forge . . . and scare the hell out of everybody . . .

"He acted like the cantakerous star he became 10 years later. He acted like he had already arrived."

Harris had a three-film deal with McQueen but canceled the other two.

With a bit of understatement about the star of Bullitt and The Thomas Crown Affair, he said, "I was never happy about that."