While one arm of the government is busy selling land to swell the federal treasury, another is buying land for the same reason. The Federal Emergency Management Agency has a "small but possibly growing program" to buy up certain flood-prone land, according to FEMA emergency management specialist Larry Zensinger.

Congress established the purchase program in 1968 as part of the national flood insurance program, but it was not funded until Congress appropriated $5.5 million in fiscal 1980. FEMA is asking Congress for $4.78 million for fiscal 1983. The agency expects that by September it will have purchased about 200 properties in 13 states.

Under the flood insurance program, the goverment said it would make flood insurance available to communities that developed plans for dealing with floods. Owners of existing properties in flood-prone areas were grandfathered in, and their insurance rates were lower than the rates paid by owners of new buildings. Zensinger said that when these areas flood the government can lose millions or billions of dollars on the low-rate homes--and they are the ones that FEMA wants to purchase. FEMA normally tears down the buildings and then turns the property over to the community for use as a public park.