The nuns who operate the Academy of the Holy Cross were shocked the other morning to receive a spate of calls from people who wanted to buy their 20-plus-acre campus just east of the Metro station on Rockville Pike. Under the cover of of night, it is suspected, some fun-loving seniors gathered up "For Sale" signs and planted them in front of Holy Cross.But it was a lark. The academy is not on the market.

L. Earl Armiger, president of MARLEA Solar Environmental Systems in Columbia, has established a solar energy division (called Sun Stone) that has a solar house under way and plans 13 more. He said that the solar energy system is a total package using air as the beat transfer medium. He has hopes of offering the dwellings in the $65,000 range.

Conrad Cafritz has taken possession of the grand old 2029 Connecticut (Avenue NW), and has set up a firm that plans to convert the 23 large units in the 60-year-old, highly stylized building into condominium ownership. All of the apartments are larger than an average single-family house and some have as many as 5,000 (yes, 5,000) square feet of space. No tenants will be asked to move before Sept. 1. Brenneman Associates is doing the marketing. Prices will range from about $85,000 to $150,000, and a major rejuvenation-improvement program is planned. The architectural trim on the exterior of the building might be impossible to duplicate today. The quality of the decorative artistry is detailed, imaginative and almost museum-like. Meanwhile, tenants whose rents have been relatively low over the years will have to face ownership costs and condo fees beginning at $350 a month.

Earlier this month the 200,000th baby was born at Columbia Hospital for Women at 2425 L St. NW. The hospital itself was born in 1866 in a former mansion on Thomas Circle NW. In 1873, according to a researcher, Congress appropriated $25,000 to buy the pre-Victorian Maynard mansion as a site for the hospital. And, despite the downturn in the birth curve, there is talk of an addition being built on Columbia Hospital.