April 19, 1997

Scientists discover precise mechanism by which HIV, AIDS virus, penetrates membrane of cells it infects; knowledge of mechanism, in which sort of spring-loaded harpoon pierces cell's surface, is significant advance and should provide drug designers many ideas for jamming harpoon, thereby averting infection; experts caution, however, that any such treatment remains a distant prospect; Dr Peter S Kim led team that discovered how HIV enters cells; photos (L)

Safeguards issued last year to prevent immigrants with criminal records from becoming citizens have largely been ignored by the agency that was supposed to carry them out, auditors said.

Many Central Americans who sought refuge in United States during 1980's are being told, as result of new immigration law that went into effect April 1, that hey must return to land of their birth; for poor countries such as El Salvador, still struggling to recover from civil wars, prospect of having to accommodate returnees--have having to do without money they send home--causes consternation; many of those who fled El Salvador, for example, have now lived in United States for up to 15 years, and have children born in US; they include applicants for political asylum, those seeking permanent residency by other means and some who still live clandestinely after entering country illegally or overstaying their visas; photo; map-table shows estimated number of illegal aliens in United States from selected countries (M)

Exhibition of Romanov jewels, along with costumes and portraits from imperial Russia, that has been on tour in United States is jeopardized, with Russian officials demanding that treasures be returned to Moscow to celebrate 850th anniversary of founding of city; exhibition has been on display at Corcoran Gallery in Washington, where it drew some 80,000 visitors; next stop was supposed to be Museum of Fine Arts in Houston; James W Symington, chmn of American Russian Cultural Cooperation Foundation, which organized visit, asserts that $2 million to $3 million is at stake in corporate and individual gifts, museum fees and other costs if rest of tour is scrubbed; photo (M)

American Assn of Retired Persons says it has revised sharply criticized plan to endorse selected health maintenance organizations, dropping proposal to collect royalty payments for each of its members who join an HMO; royalties proposal had drawn fire from Govt officials and industry experts, who suggested that it might violate Medicare anti-kickback laws; Federal laws forbid payments in cash or otherwise for referrals of Medicare beneficiaries (M)