Ex-liberal calls for grass-roots action; Nothing Can Be Done, Everything is Possible, by Byron Kennard. Andover, Mass.: Brick House Publishing Company. 180 pp. $9.95 (paperback).

The early 1980s are the era of liberal introspection. Senators such as Paul Tsongas (D) of Massachusetts and Gary Hart (D) of Colorado have challenged the ideas and political postures behind longstanding liberal policies on defense, the economy, and a range of other issues.

In ''Nothing Can Be Done, Everything Is Possible'' Byron Kennard brings that introspection to a personal level and argues convincingly, with sensitivity and humor, that liberals must first change themselves if they have any hope of changing the system. Such a catharsis will come from a renewed commitment to community organizing, the wellspring of so many progressive reforms in the past.

Byron Kennard is a fixture in populist politics. He was one of the principal organizers of the first Earth Day in 1970 and of Sun Day in 1978. But he is best known in the political community for his nationwide network of citizen activist contacts and his ability to generate a flood of phone calls and telegrams to politicians and bureaucrats when an important decision is pending.

''Nothing Can Be Done, Everything Is Possible'' is a series of essays on his life as an organizer, and more importantly, Kennard's insights into the essence of those precious few individuals willing to invest their efforts in trying to improve the world we live in. Some of the titles of these 27 short, spritely essays reflect the range of Kennard's iconoclasm: ''Don't Confuse Me With Facts, '' ''Where Are the Robber Barons Now That We Really Need Them?'' ''When Nobody Was Looking, Our Side Won'' and ''Small Is Inevitable.''

The reader will find few profound observations about the human condition here , but much that is profoundly human. ''The course of every intellectual if he pursues his journey long and unflinchingly enough,'' said Aldous Huxley, ''ends in the obvious, from which the non-intellectuals have never stirred.'' Kennard's theme is that liberals are out of touch with this ''wisdom of the ordinary.'' The housewife and the hippie, the feminist and the ecologist have much to teach professional politicians about the changes needed in America and how to achieve them.

''Efforts to restore liberals to power simply do not possess the same chance for success as community organizing,'' Kennard observes. ''Liberalism has been discredited, in part, because liberal politicians were so hooked on centralization. They wanted, sincerely, to use central authority to achieve their vision of society. They blew it and while I hate to see them go, having been a liberal myself once upon a time, in some ways they deserve the opprobrium they have fallen into.''

The author would be the first to admit that he is an organizer, not a writer. At times his ideas tumble forth so readily the reader desperately wants to call a halt so that new insights can be fleshed out. But on the whole the essays are remarkable in that they flow one from the other without the drawbacks of many collections.

Byron Kennard has written a primer for the modern-day activist. Unlike the late Saul Alinsky, who crafted principles of organizing, Kennard has drafted principles for organizers, a much more delicate task. Holding a mirror up to the personality of the citizen activist, he offers sage advice on keeping the world in perspective when dealing with the overwhelming, sensitive ego one often sees reflected there.