Ever wonder why PBS, which isn't a commercial broadcast network and is therefore immune from the ravages of advertiser-friendly sweeps periods, often schedules its highest-profile stuff in months where competition is the stiffest?

Why pledge periods usually follow sweeps periods, so that just when you'd rather scratch out your own eyeballs than watch one more rerun of "Law and Order," there's nothing on your local PBS station but infomercials and programming aimed at tapping the pocketbooks of a check-writing few?

TV critics wonder these things, too, which is one reason they migrate west every six months to put the questions to PBS president Pat Mitchell and her fellow executives.

"It's not about playing a game of ratings. It's about finding the right place for the programming," Mitchell insisted after a question that even the reporter asking it described as flogging "the familiar dead horse."

Apparently Mitchell and her staff's decided that Nov. 2 and 9 - part of a sweeps period - is the right place to showcase its remake of "Dr. Zhivago," a miniseries that PBS clearly considers pretty special.

If you remember the original, there's a lot of snow in "Dr. Zhivago." Why not play it in December, when it gets pretty chilly on the six other broadcast nets?

Because that might leave Suze Orman and that wrinkle-cure guy out in the cold.

"The same rationale you're using about [getting high-profile programs] out of harm's way was applied to the pledge program," John F. Wilson, a PBS senior vice president, told a reporter who asked why the network couldn't just move pledge periods into sweeps instead.

As long as most local PBS stations derive nearly 50 percent of their funding from pledge drives, no one should expect to see them go, Mitchell said.

"Pledge works," she said.

So what to tell viewers who'd rather not see the programming they turn to PBS for pre-empted two months a year for what you and I call infomercials and Mitchell calls "transactional programming"?

Well, apparently they need to attach letters to their checks.

Wilson, who's worked at a PBS station - KAET in Phoenix - said that what used to get HIS attention was "hearing from a contributor who said, 選'm sending you this check because I like 閃asterpiece Theatre.' I like 糎ashington Week.' I like 賎reat Performances.' I like 禅he Newshour.' That, to me, sends a signal," he said.

"So, one of the best ways for your readers to make a difference is to let the station know by voting with their contribution and say, 選 like the regular stuff. Keep it coming.' "

Or, of course, you could just order HBO, another commercial-free network that puts on pretty good programming year round for anyone who's willing to write THEM a check.