The Senate, acting to save "hallowed ground" from developers' bulldozers, has voted to protect the headquarters' site of Gen. Robert E. Lee in Manassas, Va., from being turned into a giant shopping mall.

In what has been dubbed "the second battle of Manassas," the Senate voted 50-25 late Friday night in favor of a fact-packed, eloquent and sometimes emotional appeal to take the land by legislative fiat."My colleagues, it is now or never," Sen. Dale Bumpers, D-Ark., told a hushed chamber. "We will not get a second chance. The bulldozers are there now."

Bumpers and Sen. John Warner, R-Va., converted the Senate chamber into a history classroom, with maps showing stages of the 1862 battle, and presented cases for the government to take either a limited 80 acres of the site or the whole 542-acre area where Lee pitched his headquarters at Stuart's Hill.

The measure, approved by the House in August by a resounding vote of 308-97, was attached to a technical tax law correction bill.

The complete bill is expected to pass in a Senate vote Tuesday, and differences with the House version must be settled in a conference of members of both chambers. President Reagan must sign the bill into law before the proposed development is stopped.