The Congressional Budget Office estimate of the cost of the war in Yugoslavia assumed that U.S. aircraft are flying 2,000 sorties per week in the Balkans. A story yesterday incorrectly reported a different time frame.

Bill Kirchen will perform at the Birchmere Friday; the day was incorrect in a record review in yesterday's Style section.

An article in yesterday's Business section misstated the reason Microsoft Corp. plans to defer $400 million in revenue to subsequent quarters. The company is taking the step to account for free upgrades to its Office 2000 software package that it has promised some buyers of the current version of that product, Office 97.

In some editions yesterday, an article about the proposed merger of Radcliffe College and Harvard University incorrectly identified the number of female undergraduate students. A total of 3,071 female undergraduates will be enrolled directly in Harvard when the merger takes effect; of those, an estimated 783 will graduate in 2001.

An article yesterday incorrectly identified the agency that manages the Surveillance, Epidemiology and End Results (SEER) program, which collects data on the incidence of cancer. It is run by the National Cancer Institute at the National Institutes of Health.