Judd Gregg is perplexed. The 34-year-old lawyer from Greenfield, N.H., has waded gamely into the arcane vocabulary of arms control. He can talk about verifiable reductions, equivalent megatonnage and MIRVed SLBMs.

But, in the end, he wonders aloud, "Are we doing a bit of a dance here?"

As one of New Hampshire's two congressmen, the freshman Republican must decide whether to vote today for one of two resolutions. One, sponsored by Foreign Affairs Committee Chairman Clement J. Zablocki (D-Wis.), calls for a "mutual and verifiable freeze on and reductions in nuclear weapons." It is endorsed by Democratic leaders and the national freeze movement. The other, sponsored by Rep. William S. Broomfield (Mich.), ranking Republican on the Foreign Affairs Committee, and supported by President Reagan, calls for "an equitable and verifiable agreement which freezes strategic nuclear forces at equal and substantially reduced levels."

The dance, Gregg suggests, "revolves around ego"--the ego of both sides. "Some people think by passing one resolution or the other that you're for civilization or against civilization," Gregg said. "How absurd!"

Neither resolution would have the force of law. However, the personal involvement of Reagan and House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) on opposing sides has considerably raised the political stakes. And nuclear freeze advocates, who are campaigning to put the issue up for ballot referenda in nine states, say they will hold politicians accountable in November's congressional elections for today's vote.

Gregg's vote could be crucial. According to one count yesterday, Zablocki had 193 votes lined up and Broomfield another 193, with more than 40 undecided.

In the shorthand analysis of House members, the issue boils down to Zablocki's "Freeze now--reduce later" or Broomfield's "Reduce now--Freeze later."

Freeze advocates contend that the United States and the Soviet Union must immediately stop making new nuclear weapons before they can reduce arsenals they have already accumulated. Reagan argues that the United States must increase its arsenal to give the Soviets an incentive to negotiate reductions.

In a burst of last-minute lobbying, Reagan yesterday called a score of undecided House members to the White House to meet with him, Secretary of Defense Caspar W. Weinberger and Secretary of State George P. Shultz. A few hours later, O'Neill, accompanied by Sens. Edward M. Kennedy (D-Mass.) and Mark O. Hatfield (R-Ore.), sponsors of the immediate nuclear freeze measure in the Senate, held a news conference in front of the Capitol.

Freeze resolutions passed by 34 towns in Gregg's district this spring, and the version he introduced April 29, called for "a mutual freeze on the testing, production and deployment of nuclear weapons."

Gregg said the issue is "the second most important issue in my district after the economy." He has received 400 letters on the subject.

Gregg has not been lobbied by advocates of the Zablocki resolution. But he did get a call from a White House lobbyist and a "Dear Judd" letter from Reagan--the same one 434 other House members received--which said the Zablocki freeze would leave "dangerous asymmetries in the nuclear balance" and "seriously undercut our negotiating position."

Before voting, Gregg, who usually votes with the president, said he'll listen to the floor debate and "see if there's something below the smoke."