A two-year Justice Dept. probe of admissions practices at two dozen elite colleges seems to be nearing a successful conclusion. Sources close to the investigation say that the schools, including such top-rank institutions as Harvard and Princeton Universities, won't admit to any wrongdoing. But they will agree to stop sharing information on financial aid, tuition, and faculty salaries. Justice officials, who began the probe in the wake of Administration criticism of soaring tuitions, felt that the schools violated antitrust laws by using shared information to parcel out financial aid to incoming students. Specialists within the department see the case as an indication that the government is prepared to enforce antitrust laws vigorously against nonprofit institutions.