David Clyde was in Boston the past weekend. Although the Red Sox trimmed both him and the Texas Rangers Thursday night, 4-2, his coolness over a six-inning stint was remarkable and even impressed the partisan 31,000 present at the 18-year-old's Hub debut.

In the Rangers' clubhouse before Sunday's rain-delayed and shortened game, Clyde was equally poised. The handsome, tanned pitcher has about him the bluff laconic modesty of the stereo-typed seasoned pro, rather than the open, freckled brashness of the fancied rookie. He scoffs at the suggestion that he may prematurely have fixed on a career. "It's a great life," the veteran of three weeks emphasizes. And you can't help but envy his quick ascent into the glamorous, double-knit majors.

"The guys on the team have made it, from the word go, very easy to fit right in and feel like one of the team members," Clyde said, noting that he has encountered no resentment from his cronies for his generous dolings of ink.

With the same offhanded shrug, he dismisses the spectre of such early-squandered arms as Bob MacCool and Wally Bunker. "It doesn't bother me. I'll just go out and do my thing once or twice a week. They're taking good care of my arm."

On the other hand, the pressure on Clyde to be "great" and the sudden stock in his future that baseball seers throughout the game have assumed, to the point of offering free advice, have apparently not fazed him. "I don't feel the pressure; I expect a lot more out of myself," he owns in a deadpan.

Pitching coach Chuck Estrada and manager Whitey Herzog are not taking the matter quite as lightly as Clyde is. They are mollycoddling the phenom's arm, curbing him to 6-inning performances.

Clyde acknowledges that the change in lifestyle is his most difficult adjustment, and he still has not learned to chew tobacco. In the off-season he will attend Texas A. & M. and major in journalism and television sportscasting. He explains, "If I don't make it on this side..."