"Basically, I had reached my 50th birthday and I decided that no matter how much yogurt I was going to eat I wasn't going to see another 50 birthdays. I just really decided that every day and everything I do would only be filled with things that were important."

That's how flutist Herbie Mann, talking from his New York home, explained the change in musical direction he underwent two years ago.

"I found that a lot of that music--what's called jazz fusion today--is very unimportant, very temporary and very boring. I started my own record label, and I'm playing music I want to play."

Mann's quartet will open this summer's National Parks program at the Carter Barron Amphitheatre 8:30 Saturday night. Among the other scheduled performers this season are Angela Buffel, the Manhattans, pianist Ruth Laredo, violinist Eugene Fodor and the Billy Taylor Trio with the D.C. Youth Orchestra. Cosponsored by the Anheuser-Busch Co. and the D.C. Department of Recreation, the series is free and tickets are available at Carter Barron until performance time. (For information on other ticket outlets, call 426-6943.)

"The whole band is plugged in except the drummer," Mann said, "and I'll be using echoes and a chorus machine--all my toys." The others are guitarist Lou Volte, bassist Frank Gravis and drummer Buddy Williams.