CBS' 13-hour mini-series "Space" wound up its five-night run on the network last week with an overall national Nielsen rating of 16.8 and a 27 percent audience share . . .

That ranked it 10th among the 11 mini-series that aired during the regular season on all three networks, well ahead of the season's worst-rated (NBC's "The Sun Also Rises," with a 12.4/19) but far behind "Fatal Vision," the NBC entry last November that finished on top for the year among mini-series with a 31.1/47 . . .

The annual Arthritis Foundation telethon, which was unable to get an outlet in this area last year, will be seen Sunday on Channel 45 in Baltimore between 1 p.m. and 7 p.m. . . .

Some 65 stations nationwide will carry this year's telethon, which last year raised about $2 million around the country . . .

This year's telethon will feature a country music format . . .

In Virginia, donors will be able to make their pledges Sunday by calling 703/276-7555 (that's 703/276-7555) and in the Baltimore area the number will be 301/462-5810. That's 301/462-5810 . . .

"The Best Times," which began a six-week run on NBC Friday night in the 8 p.m. time slot, didn't set any records against the ABC sitcom lineup but finished second in its time slot for the night, anyway, with a six-city Nielsen average of 10.2/18 . . . The critically aclaimed series about some attractive kids and their teachers in a Southern California high school also showed marked improvement during its second half-hour in all six markets surveyed . . .

Incidentally, Seth Freeman, the executive producer of the new series, taught math and English here at the Edmund Burke School, a private school for seventh- to 12th-graders headed for college, back in 1968-69 when it was just getting started over on Kalorama with an enrollment of about 35 students . . .

An expanded Edmund Burke, with 245 students, is now located on Upton Street NW . . .

Freeman said yesterday that his teaching experience here helped him while putting the school series together. "It was a traditional school but it had a very relaxed atmosphere" . . .

Freeman, who was calling around yesterday at the behest of Lorimar Productions, which has hopes for the show, said NBC probably will decide the future of "The Best Times" next week . . .