The best team in pro basketball last year is this year's Boston Celtics; no changes. Coach Red Auerbach has the same superb combination of youth and experience, speed and height, savvy and stamina that swept to the eastern title by six games, eased up, and then beat the inspired Hawks in the playoffs. Playing in only 48 games (out of 72), Russell was still fourth in the league in rebounds, one reason for the great success of Boston's fast break. Another, of course, is Bob Cousy, who can move faster with the ball than most pros can without it, spot a free man (or a soon-to-be-free man) with the merest corner of an eye and get the ball to him pronto. Add Bill Sharman, league leader in free-throw accuracy and a .400-plus hitter from the floor, and Tom Heinsohn, who earned his Rookie-of-the-Year award with a variety of spectacular shots. Finish with Jim Loscutoff, all spring and muscle under the boards, and you have, quite possibly, the best combination ever assembled on a pro team. Bullish Frank Ramsey and steady Arnie Risen, Andy Phillip and Jack Nichols make up a powerful bench. Only cloud on the Celtics' horizon is the advancing age of their veterans. But balancing this is Auerbach's concentration on conditioning and the pride that Sharman, Cousy, Risen and Phillip take in keeping in shape. Barring injuries to these older stars, who might recuperate slowly, the Celtics should again finish 1st.