Two buildings have been demolished and a third is clad in construction shrouds on the northwest corner of Fifth Avenue and 36th Street.

The addresses at 396, 398 and 400 Fifth Avenue, an assemblage that Joseph Chetrit has recently agreed to sell to Yitzhak Tessler for about $150 million, according to published reports.

Mr. Chetrit and Mr. Tessler are partners in the current conversion of the formerly Helmsley Windsor Hotel on the southwest corner of the Avenue of the Americas and 58th Street to the Windsor Park condominium apartment building.

Previously published plans for 400 Fifth Avenue indicated a condominium apartment tower of about 50 stories or 600 feet designed by Peter Magill of Skidmore, Owings & Merrill that featured a very unusual facade of undulating faceted elements and slightly angled windows. The tower in that plan would be setback on a base that held to the building line on Fifth Avenue.

Mr. Chetrit's office said today he was out-of-town until next week. Mr. Magill was also out-of-town, but Kim Van Holsbeke of Skidmore, Owings & Merrill indicated that the previously published plans were still active in terms of general massing but details were being reviewed because of the change in ownership.

The tower would be the latest new high-rise building to be erected within a few blocks of the Empire State Building, which has for decades stood in splendid isolation. Its site is across the avenue from 425 Fifth Avenue, a quite tall, yellow-and-white, apartment tower and it is three blocks north of 325 Fifth Avenue, a 50-story condominium apartment building now in construction.