A medium-rise, 400-room luxury resort hotel and conference center to be operated by a major chain and a-3 million-square-foot office park will be started this year on 130 undeveloped acres at Shirley Highway and Seminary Road as the final phase of the vast mixed-use development by Mark Winkler Management Inc.

According to conservative estimates, the last remaining parcel of more than 400 total acres acquired by the late Mark Winkler in 1938 is now worth a thousand times more per acre than the original purchase price-probably in the range of $100 an acre.

Over the years, several thousand rental high-rise apartments were developed on parcels of the original tract: the 2,000-unit Southern Towers complex by Preston Caruthers and George Snell (with a Winkler interest) and also the Seminary Towers site (on the east side of Shirley) that was sold to another high-rise developer.

In addition, in the 1960s and early 1970s, the Winkler group itself built more than 2,400 Hamlet rental garden apartments which have been retained. Winkler recently also has developed a modern shopping center and the five-building Mark Center I office park-300,000 square feet of preleased office space that will be completed this fall.

In addition to demonstrating the long-range vision, planning and follow-through of Mark Winkler, who died in 1970, this strategically located Northern Virginia community is also unusual because there is no plan to convert the 2,400 moderate-range rental apartments to condominiums.

The Winkler group is planning to use the remaining 130 wooded acres as the site of a big hotel and office park complex. According to Alexandria commercial zoning obtained in 1952, the site could have been developed with more than 17 million square feet of office and commercial space. Instead, plans call for use of only 15 percent of permitted density and for keeping 80 wooded acres as a park with lakes, trails, streams and other recreational uses.

Since 1970, Harold (Hal) Winkler, a brother of Mark, has been chairman of the board of the Winkler organization. Robert T. Gates, with 13 years of service, is president. Charles E. Hudson, a 12-year veteran, is executive vice president. Catherine Winkler, widow of the original developer, maintains a major ownership position and an ongoing interest in development.

"We are projecting in terms of tennis, horseback riding and swimming to make weekend vacation bookings desirable," Harold Winkler said.

Gates said that the Winkler group plans to continue its office building construction program later this year and itself become a tenant in the fifth Mark Center I building that will be completed in November.

Hudson pointed out that the Winkler organization was started in downtown Washington, where the firm still owns an office building at 1625 K St. NW and a rental apartment (the Presidential) at 16th Street and Florida Ave. NW.

The Winkler executives also said that no new rental apartments have been built at the Mark Center/Hamlet site around Seminary Road and N. Beauregard Street since 1974. "It's just not feasible under today's construction costs and rental rate patterns," Hudson said.

He estimated that the total property development on the 400-acre site now has a value well in excess of $100 million and that the total value will likely exceed $250 million after completion in the mid-1980s.

Sasaki Associates Inc. was the architect for building facades of Mark Center, according to Hudson, and Keyes, Condon and Florance of Washington did the site planning. The architectural team also included Dewberry, Nealon & Davis of Northern Virginia and Montague Associates of Washington. Eugene Simpson & Brother Inc. has handled general construction contracts. The Winkler firm handles its own leasing and management.

Recent full building tennants in the first phase of Mark Center have included the Center for Naval Analyses, Control Data Corp. and Potomac Research Inc.