Nuclear freeze advocates in the House yesterday barely fought off a weakening amendment to their resolution on a 211-to-204 vote, then agreed to some lesser changes to accommodate opponents.

During a day of desultory discussion, with little of the impassioned rhetoric that accompanied the opening of the freeze debate last month, Republicans and conservative Democrats continued their efforts to sink the freeze in a morass of technical arguments over strategic weaponry.

Each side claimed victory after the day was over.

"We have strengthened the resolution," said Rep. Newt Gingrich (R-Ga.). Rep. William Carney (R-N.Y.) said that, "If we can get one or two more substantive amendments, many of us who have opposed it would be inclined to support it."

However, a principal sponsor of the freeze, Rep. Edward J. Markey (D-Mass.), claimed, "We won every vote we wanted to win," and dismissed the new language in the resolution as "superfluous, but not incompatible."

The freeze resolution calls on President Reagan and the Soviet Union to negotiate an "immediate, mutual and verifiable freeze" on the production, development and deployment of nuclear weapons. It is strongly opposed by Reagan, who says it would undercut his Strategic Arms Reduction Talks (START) in Geneva, which are aimed at reducing the weapons totals on both sides once the United States builds up its military position.

The amendment defeated yesterday was sponsored by Rep. James G. Martin (R-N.C.). It would have required arms-control negotiators to give "special attention to destabilizing factors in the nuclear balance, including relative ages of weapons and their rates of obsolescence."

Martin and other freeze opponents argued that many weapons in the U.S. nuclear arsenal are outdated and that the Soviets have built new systems in recent years. They want to be able to build more nuclear weapons, rather than freeze at current levels.

Freeze supporters, however, said that the United States is ahead in many areas and that a freeze is fair because, on balance, the two superpowers have a rough equivalence in strategic capability.

Democratic leaders have sought to make the freeze a political issue to use against Reagan and his fellow Republicans. Only 21 Republicans joined 190 Democrats in voting against the Martin resolution, while 62 Democrats and 142 Republicans voted for it.

Locally, Virginia Republicans Stan Parris and Frank Wolf voted for it, as did Maryland Reps. Beverly Byron (D) and Marjorie Holt (R). Maryland Democrats Steny Hoyer and Michael D. Barnes voted against it.

Late in the afternoon the House opened debate on another divisive amendment, which both sides predict will produce a close vote today. Sponsored by Carney, it states that a freeze would not prevent the United States from deploying Pershing II and cruise missiles in Europe, as provided by a December, 1979, NATO agreement.

The issue of intermediate-range forces to protect Europe against a battery of threatening Soviet missiles already aimed at allied nations is a touchy question. Rep. Henry J. Hyde (R-Ill.) said that he was "shocked" to see freeze supporters "selling out NATO."

Rep. Stephen J. Solarz (D-N.Y.) sponsored a motion to add language to the Carney amendment saying that the resolution would not prevent the United States from carrying out the 1979 agreement "unless an agreement is reached with the Soviet Union, after consultation with our NATO allies, establishing a mutual and verifiable freeze which includes such intermediate range forces and corresponding Soviet forces."

In an ultimately futile effort to wind up debate on the entire resolution before a Democratic congressional dinner last night, freeze supporters, led by Foreign Affairs Committee Chairman Clement J. Zablocki (D-Wis.), accepted a series of amendments sponsored by opponents.

They included one sponsored by Rep. Samuel Stratton (D-N.Y.) saying that negotiations must provide for maintenance of a vigorous research, development and safety-related improvements program to ensure that the United States is not limited to levels of nuclear-deterrent forces inferior to the Soviet Union.

Originally, Stratton's amendment would have allowed "modernization" of U.S. forces, a code-word for Reagan's $1.6 trillion military buildup. But Zablocki, on a voice vote, substituted the words "safety-related improvements."

Other amendments expanded the freeze to anti-submarine warfare and anti-bomber defense systems.

While proponents said the Stratton amendment was a significant change in the resolution, Markey called it "gobbledygook." By adding that and other amendments, freeze opponents were "protecting their political hides," he said. "They've seen the latest Lou Harris poll showing that by 79 to 13, the American people favor the freeze . . . . Now they can go home and say, 'We feel better about the freeze since they've accepted these amendments.' "

Hyde, however, ridiculed the freeze proponents' motives as political, saying, "They've suddenly discovered the atom bomb, which has been in existence since Aug. 6, 1945."