If a Tantallon entrepreneur has his way, Prince George's County may have the first 24-hour day-care center in the Maryland suburbs by Thanksgiving.

Prince George's officials say they are close to leasing the closed Thomas Addison Elementary school in Oxon Hill to lawyer Nelson Williams, proprietor of Knee-Hi Nursery Inc.

The five-year lease with option to purchase will rid the county of one of 54 schools closed because of declining enrollment since 1977, and bring Williams close to realizing a two-year-old dream.

"By the 1990s one of every two homes will be a one-parent family, and more and more women are entering the work force," said Williams, a retired Air Force colonel. "That's why I had the idea for a 24-hour center."

The center would accommodate the parent who wants to go shopping and the parent who wants to work the swing shift, Williams said, noting that many day-care centers charge stiff penalties for parents who pick up children after the usual 6:30 p.m. or 7 p.m. closing.

The nursery, which must get licensing and zoning approvals from the county, plans an enrollment of up to 400 children between the ages of 2 and 8. The large size, according to Williams, will create economies of scale that make 24 hours practical.

Donald Ellis, a county school official in charge of marketing the ever-growing inventory of vacant county schools, admitted that the idea was "unusual," but said that it could work.

"Suppose I were working midnight to eight and I was a single parent, that would be the place to be," said Ellis, who still has a dozen schools on hand for sale.

As school enrollment in Prince George's plummets from a high of 162,000 in 1972 to 110,000 this year, the surfeit of closed schools presents a unique problem for the county. Many are located in the heart of subdivisions, limiting what they can be used for, while idle schools are an easy target for vandals.

Some buildings, especially those located in commercially viable areas, have been sold as office buildings, a medical center, a nursing home and a church school.

Most elementary schools sell for approximately $500,000 with 30 percent down, but the county was willing to lease the Addison school for $750 per month until Williams is able to purchase the school outright.

Williams took care to point out that his 24-hour concept should not be confused with "the Orwellian thing where the state takes over your children."