To compare the virologic response between abacavir (ABC, 1592U89) regimens (drug vs. placebo) and between the 2 dosing regimens (BID vs. TID) with respect to the proportion of patients with plasma HIV RNA levels below the limit of detection [AS PER AMENDMENT 8/27/97: < 500 copies/ml at week 16]. To evaluate the safety and tolerance of the study arms. [AS PER AMENDMENT 3/10/99: During the extension period, compare the time to detectable viremia (2 consecutive plasma HIV RNA levels greater than or equal to 500 copies/ml) between ABC and placebo.] Therapeutically, there is a need to explore potent alternative therapy for patients who have received, or are currently receiving, a double nucleoside analog combination including lamivudine (3TC), a regimen that was proven to be clinically inferior to indinavir (IDV) when combined with zidovudine/3TC in study ACTG 320. In order to produce and maintain a maximal antiviral response, all patients in this study will receive 2 or 3 potent, new agents; ABC, a nucleoside analog, EFV, a non-nucleoside reverse transcriptase inhibitor (NNRTI), and IDV, a protease inhibitor. Virologically, the major question this protocol seeks to answer is how prior 3TC exposure in a dual nucleoside regimen influences the response to subsequent treatment. It is unclear whether it is best to add a protease inhibitor either 1) an NNRTI at 1 of 2 doses, or 2) an NNRTI at 1 of 2 doses plus a new nucleoside analog to achieve plasma HIV RNA levels that are below the limits of detection.