The U.S. Navy, which cruises the Seven Seas at will, is being blocked from crossing the paltry Potomac River in what is shaping up as a classic American political battle.

At stake are 17,000 Navy employes currently working in Northern Virginia whom the Navy wants to relocate to its Washington Navy Yard in the District of Columbia. Opposing the move are five Virginia members of Congress.

For the moment, it looks like The First Battle of the Potomac has been won -- in rather impressive style -- by the congressmen.

Like most battles fought along the banks of the Potomac nowadays, the rallying cry is savings to the taxpayer. The Navy, for its part, says it is merely trying to save American taxpayers up to $73 million by surrendering leased office space in Northern Virginia for Navy-owned, rent-free space at the Washington Navy Yard in Southeast.

Virginia politicians, for their part, have challenged the Navy's figures and warned that the additional traffic that would end up crossing the already crowded Potomac River bridges would jam them even more.

So far, political clout on key congressional committees has won out over the Navy's bureaucracy and the abilities of District of Columbia politicians, who view the prospect of increased employment in the District as a boon.

A vivid demonstration of that clout took place when Sen. John W. Warner (R-Va.) discovered last year that the Navy was seeking $15.4 million in this year's military construction authorization bill for first-stage construction and renovation work on the five-year project, which would cost a total of $280 million.

Warner, a former Navy secretary, and Rep. Paul S. Trible Jr. (R-Va.) won a deletion of the funds in both the Senate and House Armed Services committees after charging that by trading the 1.9 million square feet of Northern Virginia office the Navy currently occupies for the Navy Yard, the Navy would cause economic and social problems for the Crystal City area and would not be cost effective.

"I have personally strong reservations about the Navy's proposal, not just because of its impact on the Northern Virginia area, which would be significant, but because, to date, the Navy has not made a good case for the move," charged Rep. Frank R. Wolf (R-Va.), who quickly joined forces with Trible, Warner and Rep. Stan Parris(R-Va.).

Added still another Virginia opponent, Sen. Harry F. Byrd Jr. (I-Va.), a member of the Senate Armed Services Committee:

"I am unequivocally opposed to the move . . . and would oppose any further effort in that direction," Byrd said. "The move would add an equivalent of an army division -- 18,000 persons -- to rush-hour traffic going in and out of the District daily."

The Virginia delegation said Navy cost estimates are flawed.

The Navy views the Virginians' victory as only a temporary setback and is still hoping that members more friendly to its cause will reinsert the $15.4 million.

"We have not changed our mind," said Cmdr. William F. Burke, Navy facilities planning director for the Washington area. "We want to move."

"The fight is not over," vowed Walter E. Fauntroy, the District delegate to the House of Representatives. "I will continue to work with the Navy to encourage the consolidation of sites, not just as a parochial matter, but based on the belief that it would save the federal government approximately $70 million."

So far, the Navy's way of fighting back against opponents of the move has been to fund three recent studies that they say confirm that rents for its leased space in Northern Virginia eventually will skyrocket. The argument is not a new one.

The Navy has had its eye on the Yard for office space since 1966 when the facility ceased being used to make naval guns. Studies then contemplated transforming the aging industrial Navy Yard into an office complex for 10,000 Navy employes. For its part, the General Services Administration, the government's housekeeping agency, planned a Southeast Federal Center that would employ another 20,000 workers. Congress never funded either plan.

In those days, 12,000 Navy workers were housed in dilapidated, World War I vintage "temporary" office buildings along the western end of the Mall from 17th to 23rd streets NW. Eventually, even presidents complained about their appearance. After he became president, Franklin D. Roosevelt -- who had ordered their construction in 1917 when he was Navy undersecretary -- said they were an embarrassing eyesore.

Finally, Richard Nixon ordered that they be torn down in 1969 and they were razed in a few months.

GSA, which handles government leasing, then had a policy to rent rather than build government office space. GSA turned to Crystal City, then emerging on the Arlington skyline.

So, with GSA footing the rental bill and Nixon making the decisions, the Navy moved.

Within the decade, however, government policy reversed again. Today, GSA's mandate is to build and own government office space because it is said to be cheaper than renting. Congress has also passed a law requiring GSA to charge agencies fair market value for both government-owned and government-leased office space.

These policy changes again compelled the Navy to come to the same conclusion: Much of the Navy Yard should be developed as office space.

Currently, the Navy controls about half of the Navy Yard space that it wants to develop after having turned over the remainder to GSA for disposal years ago when earlier construction plans fell through. The Navy now wants to make that severed 60-acre parcel part of a military installation again, where the GSA could not charge rent.

GSA Regional Planning Staff Director Jack Finberg said the agency endorses the move if the Navy can pull it off in Congress, although, he says, the GSA would "prefer" to own its land and charge the Navy rent.

Though the District has limited power of advocacy, the Navy has made it clear that combined with a GSA plan to sell two industrial blocks north of the Yard to a private developer and a Capitol Gateway Corp. plan to construct a $400 million hotel-office-apartment complex west of the Yard, the Navy Yard change would be a boon to the city.

And the feared traffic mess? Navy Undersecretary Chapman Cox has testifed the move would add only 900 autos to traffic going into and out of the city every day. He said many Navy employes who live in Virginia would carpool or use public transportation.

"We would hope," Burke said, that a $500,000 Navy environmental impact study due out in November will show little "adverse, unmitigatable environmental impact" on traffic flow. The EIS also will address economic impacts on the Northern Virginia economy and social impacts in the community near the Navy Yard, Burke said.

But all of this is secondary to what the Navy says is its main worry -- money. Until 1975, the Navy, like other federal agencies, was not charged for office space because GSA paid all government rents to private landlords. When that changed, Navy rent in Crystal City went overnight from zero to an estimated fair-market rent of $8 million a year.

By 1981, the Navy rental payment to GSA for the space involved in the proposed move had increased to $19.6 million a year. But because GSA still held long-term leases at much lower rates, GSA paid the landlords only $14.6 million. The $5 million difference landed in GSA's public building fund, where it could be used to build and maintain non-military government buildings.

The Navy may still have a few tricks up its sleeve. For instance, Burke said the "phase one" funding that was killed was carefully crafted to be "organizationally, economically and environmentally independent" of the other phases of the plan. Because the Armed Services committees did not formally disapprove the overall plan, he said, the Navy is not interpreting the defeat as a rejection of its overall construction plan for the Yard.

All the same, the Virginia congressional delegation remains confident.

"Given the often professed need for real improvement of naval fighting power," testified Wolf, whose district includes Crystal City,"the Navy has a difficult burden to meet to justify spending this amount of money on new office space."