The Navy, which left dilapidated temporary quarters on the Mall in 1970 to move into sleek new offices in Crystal City, plans to ask Congress for $172 million to build new offices at the Washington Navy Yard, Sen. John W. Warner (R-Va.) said yesterday.

The Navy would relocate 18,000 of its civilian and military employes from its leased offices in the Northern Virginia suburbs to the Southeast Washington compound where huge naval guns once were manufactured.

According to congressional staffers present at a meeting with Navy officials yesterday, the Navy plans to announce this morning both a $2 million environmental impact study of the proposed move and the possibility that construction could be completed within the next six years.

Navy officials would not comment on the proposal, but congressional aides said the Navy told them it expected to "break even" within 12 years on the difference between renting space and the cost of new construction. y

Warner, who as secretary of the Navy under the Nixon Administration was instrumental in dismantling the "tempos" on the Mall -- some of which dated from World War I -- and moving personnel into rented quarters in the suburbs, said he would oppose the construction "when in my judgment there are already buildings up in suburban Washington."

Warner questioned the necessity of the $172 million construction at a time when the Reagan Administration is spending billions of extra dollars trying to beef up the nation's front-line defenses. "My concern is that we're so strapped for funds to meet the rediness question and the need to upgrade hardware, build new ships. . . I cannot at first glance see why the Navy is reversing course."

Warner, a member of the Senate Armed Services Subcommittee on Military Construction and Stockpiles, described the plan as "ridiculous" and "a complete surprise" and said he was "disturbed" by appearances that the Navy had known of intentions as early as last April yet did not inform Congress.

"The question is whether they were entirely forthcoming," he said.

Sen. Harry F. Byrd Jr. (I-Va.) joined Warner in denouncing the plans. "The Navy undoubtedly has better projects for the expenditure for hundreds of millions of dollars than for the construction of a new office complex in a crowded section of our city. The plan raises a host of questions," he said.

In April, Warner said, Congress received a request from the Navy for $2 million to $3 million to study possible construction at the Navy Yard but that there was "no indication of any intent to move. I cannot definitely connect the two," he said, "but it is highly coincidental."

Warner and other Virginia officials said they object to the proposal because it would add to rush hour congestion by moving employes away from already completed Metro stations to an area where the prospects for future Metro service are "dubious."

"It is ridiculous to even think about forcing 18,000 more people into the rush-hour traffic jams we already have on the Potomac River bridges," Warner said. "It would be an extreme hardship on them and would drastically worsen the situation for hundreds of thousands of Virginia commuters who already use brudges over the Potomac and Anacostia Rivers to get to and from work."

Virginia's 10th District Republican Rep. Frank Wolf, from whose jurisdiction the Navy personnel would be moving, was described by his press aide yesterday as "livid" over the proposal. Upon learning of the plan, Wolf immediately scheduled a meeting for today with Navy officials to discuss details.