BOOK REVIEW / NONFICTION : In America, but Longing for Home : SPECIAL SORROWS: The Diasporic Imagination of Irish, Polish and Jewish Immigrants in the United States <i> by Matthew Frye Jacobson</i> , Harvard University Press, $45, 336 pages

“Mother of Exiles” is what Emma Lazarus calls the Statue of Liberty in a seldom-quoted line of her famous poem, and the image suggests something strange but crucial in the saga of America as a nation of immigrants.

Jacobson, a history professor at the State University of New York at Stony Brook, focuses on three immigrant groups--the Irish, the Poles and the Jews of Eastern Europe and Russia--in “Special Sorrows,” a scholarly study of the real roots of what he calls “America’s largely assimilated but ultimately ‘unmeltable’ ethnics.” It’s a startling point of view for readers who are accustomed to the self-congratulatory myth of America as a beacon of liberty to which the “huddled masses” of the world look with longing.

What Jacobson calls “the diasporic imagination” is expressed in the politics and the popular culture of the three immigrant communities that he has studied.

Nurtured on their own national myths--and newly empowered by the material wealth and assertive politics of the New World--the immigrants became ardent supporters of the struggles for national liberation in their respective homelands.

Still, there’s an obvious contradiction at work here--America turned out to be a mostly welcoming and comforting place for these immigrant communities, and they were able to furnish moral and material support for their brethren only because America provided them the means and opportunity to do so. So the troubling question of “dual loyalty” arises: Where does the loyalty of the immigrant actually reside?

Jacobson considers the contradiction in an intriguing digression, a survey of how the Irish, the Poles and the Jews in America responded to the surge of imperialist fervor that attended the Spanish-American War in 1898. He finds “an uncomfortable double-edge” in immigrant public opinion, a nagging sense that America was merely replacing Spain as an oppressor in Cuba and the Philippines.

“The exiles identified with Cuba and found vicarious satisfaction in the island’s imminent liberation,” Jacobson reports, “and yet they wondered why the Cuban tragedy had stirred so much interest when Ireland, Poland or the reconcentrados of the Russian Pale had not.”

By the end of Jacobson’s sometimes weighty but well-argued book, the figure of liberty has turned from a symbol of welcome and refuge to an oddly distant and lonely figure, and the comforting old myths are turned on their heads.