PBS focuses skillfully on two widely different communities. In Silicon Valley, traditions date back only a few years and residents feel the pressure of new trends in the US and world economy.

Silicon Valley PBS, Tuesdays, 10-11 p.m., Aug. 25, Sept. 1, and Sept. 8, check local listings. Producer: Julie Moline. Produced by KTEH, San Jose, Calif. If there is need for proof that local television stations are capable of producing fine documentaries of importance to national audiences, this three-part series provides ample evidence.

It is a solid, incisive overview of the new gold rush in Northern California's Santa Clara Valley.

Based upon a book by Michael Malone, ``The Big Score: The Billion Dollar Story of Silicon Valley,'' the series calls upon Mr. Malone for intermittent commentary that pinpoints the overall perspective succinctly.

According to this gently probing documentary, the growth of Silicon Valley has been a love affair with high technology. ``Almost everyone came from somewhere else,'' it is explained. A disparate group of science-oriented individuals managed to turn a collection of farm towns producing prunes, apricots, and cherries into the high-tech center of the world.

Described by a venture capitalist on camera as similar to ``Florence during the Renaissance,'' the name Silicon Valley has come into general usage only since 1970.

The premi`ere program focuses on the developments over the past 80 years - the invention of the vacuum tube, the transistor, the integrated circuit, personal computer, and the micro-processor.

While the inventors are featured, equal importance is paid to the engineers-turned-businessmen who pioneered the developments. Interviews with some of these people reveal the entrepreneurial spirit that seemed to fuel scientific revelation. There are fascinating glimpses of the founders of the Apple Computer company and Atari games as well as a visit to the fabled Home Brew Computer Club at Stanford.

As activity in the valley simmers down and as the age of political activism is dissipated, a most important question is asked but not answered: ``Can Silicon Valley turn concervative without losing its vitality?''

Program 2 focuses more on the people who live and work in Silicon Valley today. Program 3 explores the challenges and opportunities confronting the valley today as the pattern of boom and bust seems to be taking hold.

Perhaps the story of ``Silicon Valley'' could have been told in two hours rather than three.

Perhaps there could have been a little tightening of the material.

But despite these misgivings, the fact is that San Jose's KTEH has presented the country with an indelible chronicle that bares not only facts about the high-tech capital of the world, but offers invaluable insight into its heart, mind, and soul.