Raymond Burr has been playing Perry Mason for nearly half of his 74 years.

The original series ran on CBS from 1957-1966. And, believe it or not, tonight's two-hour movie - "The Case of the Glass Coffin" (7 p.m., Ch. 2) - is the 20th in the NBC series."I'm not the kind of person to retire," Burr said in a telephone interview. "I bought a farm up in northern California not long ago. I would be delighted to spend 365 days a year there. But last year, I was there only 28 days."

The formula for Perry Mason has always remained pretty much the same. But demographic research shows millions of viewers who weren't even born in 1957 tune into the lawyer's continuing adventures.

"It captures the young viewers as well as the older one," Burr said. "It kind of proves out that you don't have to have a maximum amount of violence to attract an audience."

The popularity of Mason has never dimmed. The original series is still shown in reruns across the country and around the world. The Mason movies not only draw big ratings their first time out, but are being rerun - KXIV ran Perry Mason Week last week and WTBS is doing the same next week.

Burr is currently working on the 21st Mason movie, and while no more are schedule right now, you can bet some sort of new deal will be worked out.

"I've appreciated the audiences over the year," he said. "I'd like to keep doing one or two (Perry Masons) every year, but there are other things I'd like to do, too."

Without Burr, there is no Perry Mason. Which gives him a great deal of control over the production.

"I'm free to turn one down," he said. "As a matter of fact, this one replaced one I wouldn't do - a picture I thought wasn't up to par."

The producers reportedly weren't overly pleased at having to scrap a show that was already in pre-production but managed to come up with a script Burr liked.

In "The Case of the Glass Coffin," Mason defends a magician (played by Peter Scolari of "Newhart") who is charged with murder when his beautiful assistant is killed during an elaborate trick.

And Burr insisted that, rather than just a judge, a jury be included in the script. Not only that, but he wanted the trial moved to the scene of the crime.

"We moved the whole proceeding into the theater - the art deco Paramount Theater in Denver," Burr said. "The jury is sitting down in the orchestra seats and the judge is in the orchestra pit."

Burr said it even surprises him sometimes to think about how long he's been a television actor.

"Barbara (Hale, who plays Della Street) would hate to hear me say this, but we've know each other almost 50 years," he said.

"When we started doing `Perry Mason,' Barbara Hale's children were always on my knees. And on `Ironside,' two of Don Galloway's children were always on my knees. It seems like yesterday his girls were just 8 months and 18 months old. They're both out of college now.

"I'm looking for a new family."

Soon, however, he may be reunited with another of his old families. Burr is currently negotiating with Universal and NBC to do an "Ironside" reunion.