HISTORY MAY NOT always repeat itself, but its local students are braced right now for Round Four of the Third Battle of Manassas-the annual fight over preservation of historically valuable land around the Manassas Battlefield National Park. If this pageant of politics and provincialism runs true to form, it will have an unhappy ending in which the anti-preservation commercial forces in Prince William County prevail and a preservation bill dies in the U.S. Senate. But there is one important change in the cast that could make a difference: Virginia's new senator, John Warner, who so far has kept an open mind on the issue.

This year's battle opens once again with a bill sponsored by Rep. Herbert Harris (D-Va.), a measure that the House knows and loves-since it has passed versions of it on three different occasions beginning in September of 1976. Last year, bipartisan cosponsors included Virginia Reps. M. Caldwell Butler, Joseph L. Fisher, Paul S. Trible, and G. William Whitehurst. This year, Mr. Harris is seeking the understanding of Virginia's two senators before introducing a proposal. The idea is still to expand the periphery of the battlefield park to protect various sites of action, including acreage around Stone Bridge over Bull Run, where a Confederate general named Jackson acquired the nickname "Stonewall."

But over the years, a majority of Prince William County's supervisors has taken a narrower view. These local overseers have fought to leave the acreage unprotected-open to any development, no matter now disfiguring. In addition, they have argued that part of the land may be needed for a highway bypass (Rte.234); if that is so, says Mr. Harris, his legislation could provide for a right-of-way to which the Interior Department would agree.

As Virginia's junior senator before his retirement last year, William L. Scott singlehandedly blocked the bill once-by proxy, during a junket-in the closing hours of a session. Then last year, Sen. Harry F. Byrd Jr. (I-Va.), bowing to the county supervisors' opposition, blocked Senate consideration of the bill, saying that a "cooling-off period seems in order." That time should be up by now. Sen. Byrd-whose father was instrumental in moves to establish the park in 1940-has a record of concern not only for Virginia's heritage, but for conservation in general, and he could be instrumental in moving this legislation. Similarly, Sen. Warner, who directed the U.S. Bicentennial celebration, has an appreciation of history that should lead him to support the battlefield legislation. With the senator's help, the Manassas preservation bill could be enacted before the land is irretrievably desecrated.