Free Trade Agreement Gets Hung Up; Votes Still Short : Thorny issues of pay disparities and environmental regulation go unresolved. Perot attacks add to NAFTA backers’ woes.

These are dark days for the North American Free Trade Agreement, and they promise to grow darker still.

The supplemental negotiations on which the agreement hinges have run into obstacles--possibly forcing delay in sending the pact to the House and Senate for approval. Ross Perot has taken on the defeat of the agreement with Canada and Mexico as his No. 1 project. In Congress, where both houses must approve the free trade pact by a simple majority, the numbers are daunting.

Although the Senate is likely to favor NAFTA, supporters concede that they are far short of the 218 votes they need in the House of Representatives; of 192 members who expressed their opposition in a procedural vote in 1992, 140 remain in the House and are counted as anti-NAFTA votes.

“If it came to the Hill now, it would not have the votes,” Rep. Robert T. Matsui (D-Sacramento) said. “We have an uphill battle no matter how you look at it.”

The fight for congressional approval of the agreement “will be one of the real tests of Bill Clinton--whether he is a world leader or a governor,” said a Republican who played key roles in the Ronald Reagan and George Bush administrations.

” . . . It’s the maturation, or the further disintegration, of the Clinton presidency.”

A congressional aide close to the House’s Democratic leadership described what he said is “very much a fluid situation,” and expressed concern that Perot’s attacks could have a snowballing effect by crystallizing opposition at a time few new supporters are lining up behind the White House.

The Administration, he said, has “a shot, but a remote shot” at victory, and will certainly need a strong wave of Republican support to overcome those in the Democratic Party already leaning against the agreement.

But, veteran Washington vote counters in and out of Congress say it is unwise to discount the ability of the White House--any White House--to pull a rabbit out of a hat when it comes to foreign policy issues that make their way to Capitol Hill. For that reason, the White House plans to stress the foreign policy aspect of the agreement in Congress, an Administration official said.

Matsui, a senior member of the House trade subcommittee, and other pact supporters insist that the White House can win if, as one Republican with close ties to Capitol Hill said, the President is willing “to pull out all the stops.”

The vision offered by the agreement is grand: A barrier-free trading zone from the Yucatan to the Yukon, through which the fruits of factories and fields could pass to new markets in Mexico, the United States and Canada unhindered by taxes and quotas and complex licensing regulations designed to limit foreign competition with domestic industries.

The three-way pact that would accomplish this goal is complete, and negotiators hope to finish within two months the supplemental agreements intended to make sure that each country’s labor and environmental standards are honored and that individual industries are protected from sudden surges of cheaper imports. But U.S. Trade Representative Mickey Kantor has acknowledged that objections to the United States’ hard-edged demands may delay completion of these talks.

For Clinton, the battle--sandwiched almost certainly between the congressional votes on his economic plan and his proposal to overhaul the nation’s health care system--will be one of the most important of the year.

The focus appears to be on the House, where members are more susceptible to political pressure because individual congressional districts, with a more narrowly focused economic base, could be more severely damaged by the pact than an entire state.

Budget Director Leon E. Panetta, a House veteran, sent up a red flag for the agreement’s supporters a month ago, saying that its future was deeply troubled. Panetta’s remarks energized them to try to counter the opposition, which has mobilized environmental interests, elements of organized labor such as the auto workers and Teamsters, and segments of the economy that fear disaster under NAFTA--among them Florida citrus growers concerned about cheaper Mexican crops.

But the opposition most feared by the Administration is the diminutive former presidential candidate, Perot. He has lopped off half-hour chunks of network prime-time television to present his case against the pact.

At the heart of the argument against the agreement are concerns that three factors will draw jobs to Mexico from the United States because production would be cheaper there. They are:

* Average hourly compensation of Mexican workers, including wages and benefits, amounted to $2.35 in 1992, compared with $16.17 in the United States.

* Environmental laws that can make production more expensive are not enforced in Mexico as strictly as they are in the United States.

* Laws prohibiting child labor, and other laws protecting workers, are similarly skirted in Mexico.

The supplemental agreements being negotiated now are intended to even the playing field.