IT`S THE Summer of Love. Eileen is 19, at odds with her family back in Illinois, and not doing so well with her boyfriend, Nick. He regards her as "one of those women, who reveal themselves in rushing monologues." On the eve of the 1969 American lunar mission, her hippie friends stage a "moonwake" on the Pacific coast that immediately scatters them apart - sending Eileen north to British Columbia, transporting a draft dodger. That closes out the first section - and provides the vantage point - for Centre/Center (Talonbooks, 256 pages, $15.95 paper), by the Vancouver writer Mary Bums. In the novel`s final two parts (set in the ensuing two decades), Bums illuminates West Coast disillusionment, as the Mulroney government is re elected and cranks up free trade. These feelings run twofold for her American-born characters, who had conceived of Canada as a true alternative to their native country. In part three, Nick`s daughter, Tranquility, drives from their Calgary home to Seattle in search of her estranged mother, and shatters the 20-yearold myth about her father and his whole generation. Though penetrating, Bums`s muse is sometimes bogged down by her penchant for detail. And the `60s, the Kennedys, the space program, and Vietnam are all tiredout topics. Nonetheless, the force of Centre/Center`s introspective imperative makes it work.