Sen. Gary Hart (D-Colo.) took to the nearly empty floor of the Senate yesterday to warn that the navy is about to spend billions of dollars on the wrong kind of ships.

Instead of buying so many Cadillacs, such as the Nimitz aircraft carrier and the Los Angeles-class nuclear submarine, he argued, the Navy should buy more Chevrolets, such as light carriers and advanced diesel subs.

"The mahogany cheered," Hart said afterward in noting that the furniture in the chamber was his most enthusiastic audience for a speech challenging President Reagan's defense budget.

Hart's remark epitomized Congress' relunctance to criticize Reagan's plan to obligate $1.46 trillion for national defense over the next five years and actually spend $1.3 trillion of it, while reducing federal money for food stamps, college loans and medical aid for the poor.

Part of the explanation for this silence lies in the length of the political casualty list from last year's election. Such vocal Pentagon critics as Frank Church (D-Idaho), John Culver (D-Iowa), George McGovern (D-N.D.) and Gaylord Nelson (D-Wis.) are gone. Hart was one of the few liberal senators who survived the conservatives' campaign against him.

Also, Reagan sent his final defense budget blueprint to Congress on Wednesday, a week before he is scheduled to reveal the rest of his planned cuts in domestic programs. James R. Jones (D-Okla.), chairman of the House Budget Committee said yesterday that this means "we're operating on blind rhetoric" until Reagan discloses the other reductions.

Mark Hatfield (R-Ore.), new chairman of the Senate Appropriations Committee, vowed yesterday to force the Senate to look at the Reagan defense and non-defense budgets as a whole, with special emphasis on Pentagon funding increases compared to domestic program cuts.

Budget chief David A. Stockman, testifying yesterday before the House Banking Committee, said that even if Congress fails to pass all of Reagan's proposed domestic budget cuts, defense spending should be increased substantially.

Hatfield said in an interview that he had told Stockman he would lead the administration's campaign in the Senate to impose domestic cuts, so long as some Pentagon programs were reduced. Stockman provided no such list of Pentagon cuts Feb. 18 when Reagan's first set of domestic cuts was disclosed, Hatfield complained.

"I donht know of any school of economics that contends we can do all those things President Reagan wants to do -- tax cuts, raising employment, reducing inflation -- without at least some cuts on the defense side," Hatfield said.

Conceding that "I'm one of a very small minority" in making such arguments, Hatfield said he intends to call expert military witnesses to share with the committee the misgivings they have expressed privately to him about spending so much money so fast in a defense industry that cannot absorb it efficiently.

"We Republicans damned Roosevelt for years for throwing money at problems," Hatfield said, adding that he had made this point to Stockman and other Reagan advisers in recent weeks. "Now we're doing the same thing by saying if you escalate dollars, you escalate security. You can't prove that on a cost-benefit ratio."

Hatfield said the fall of the shah of Iran showed how self-deluding it is to equate weaponry with national strength.

Defense Secretary Caspar W. Weinberger said he had cut $5.48 billion out of the Carter defense budgets for fiscal 1981 and 1982. But more than half of that claimed "savings," -- $3.77 billion -- was achieved by assuming that inflation would be lower in the future than Carter had projected, a challengable assumption in light of current economic trends.