Development in Prince George's County -- an area considered by some to be the last frontier of undeveloped land in the Washington area -- is being spurred by relatively inexpensive land prices and the county's ability to serve both the Washington and Baltimore markets.

Construction will begin later this month on Phase II of the Ammendale Business Campus, a $2.5 million, 450-acre project being developed off Rte. 1 in Beltsville. When completed in 1997, the business park will have a total of 3.5 million square feet of space and will employ 8,900 people in a total of 67 buildings.

As the land developer, the Michael Cos. can either sell lots to developers or retain them for leasing.

Windsor Development is one such company that has bought land there. It is developing Phase II, a six-building, 23-acre site at 6500 Virginia Manor Rd. "We expect our first building to be completed by January of 1988," said Michael Stotz, a partner in Windsor Development. That building has been leased to Federal Express Co.

Annual lease rates at Ammendale will range from $6.75 to $11 per square foot.

In other developments in commercial realty:

Telex Computer Products Inc., a telecommunications company, leased 23,952 square feet at Point West Plaza, 8609 Westwood Center Dr., Tysons Corner, from J.A. Loveless Co. Leggat McCall was the leasing agent.

Wilkes, Artis, Hedrick & Lane, a law firm, leased 31,834 square feet at 1666 K St. NW. from the Charles E. Smith Co. Vector Realty Group Inc. was the leasing agent.