'English Only' Threatens National Unity The article ''Dole Renews 'English Only' Drive, but Is It Mostly Babble?'' Sept. 8, exacerbates the controversy between extremes in this debate. The inability to speak a common tongue does indeed threaten the unity of America. But it is ridiculous for the Mexican-American Legal Defense and Education Fund to say, ''Dole and others supporting these moves talk as if differing languages are the sole cause of strife in this country.'' Sen. Bob Dole and others are not so naive. Those who speak of the official English movement as ''English Only'' are just exploiting the chips on people's shoulders. Helen S. Ullmann Acton, Mass. Your letters are welcome. For publication they must be signed and include your address and telephone number. Only a selection can be published and none acknowledged. Letters should be addressed to ''Readers Write'' and sent by mail to One Norway St., Boston, MA 02115, by fax to 617-450-2317, or by Internet e-mail (200 words maximum) to OPED@RACHEL.CSPS.COM.