If Monday mornings are unwelcome after a relaxing weekend, imagine what they must be to Steve and Chip Baird at Citibank in Manhattan at 8 a.m.

The brothers, investment bankers, have a rather grueling hobby in their pursuit of platform tennis, a rapidly growing sport that keeps them on the road almost every weekend from October to March.

This weekend they returned to Chevy Chase, (they lives here from 1966 to 1969 when their faither, Charles F. Baird, was undersecretary of the Navy,) to play in the Middle Atlantic Platform Tennis championships at Columbia Country Club.

"i've worked for 48 days in a row, if you count as work," said Steve, 26. "At Citibank they don't care what you did over the weekend so long as you show up at 8 Monday morning."

Chip Baird, 23, figures his specialty in mergers and acquisitions makes for a 70-hour work week that often finds him arriving home 1 or 2 a.m.

"It's difficult bacause you have to think about getting mentally prepared for the next two days," he said. "And it's becoming increasingly difficult to complete against people who are fulltime pros."

The Bairds must be doing something right. They are tied for first place in the national ranking with Gordon Gray and Doug Russell in platform tennis, played outdoors on an elevated platform fenced in with wire.