Politics is about to get a new hula hoop.

It is called international trade and, as the nation's governors ended a conference on the subject today, most came away convinced that it may be the dominant issue of the 1986 midterm campaigns.

No one seemed sure which party is better positioned to run with the issue or for how long. But after three days of stories about lost jobs and blocked markets, few were ready to disagree with New Hampshire Gov. John H. Sununu (R), who said, "The monthly trade balance number is going to become the new political performance index of 1986."

Like so many Republicans in Congress and statehouses, Sununu is worried that the laissez-faire stance of the White House in the face of a projected record $150 billion trade deficit this year will set his party up for a licking in 1986.

When Treasury Secretary James A. Baker III preached the orthodoxy of free trade here yesterday, Sununu gave him the most backtalk. "A lot of us who are free traders are getting awfully impatient with the lack of reciprocity," he said.

When Baker argued that the deficits can be viewed as a testimonial to U.S. economic growth and stability, Sununu drily observed: "You're telling us that the reason things are so bad is that they are so good, and they will get better as soon as they get worse."

"You got it," Baker said, seemingly eager to move on to another question.

If the trade issue makes Republicans nervous, it also catches the Democrats off balance.

"Yes, it's a major major target of opporunity, but I am not sure we have figured out how to exploit it yet," said Virginia Gov. Charles S. Robb (D).

As the "out" party, the Democrats do not have to take the heat for trade-related job losses in agriculture, steel, mining and computers. But if they push protectionism too hard, they could be tagged -- as they were in 1984 -- as the party of special interests.

There was little support among Democratic governors here this week for a Democratic trade bill that would impose a 25 percent tariff surcharge on imports from Japan, Brazil, Taiwan and South Korea unless they cut their U.S. trade surpluses by 5 percent.

"That's a meat ax," said Massachusetts Gov. Michael S. Dukakis (D). "We need a scalpel."

Despite their readiness to wave the flag, plenty of Democratic governors disapprove of protectionism. "It may be attractive in the short-term," said Florida Gov. Robert Graham (D), "but it is a policy for long-term devastation. Florida, for one, would be hurt by a retreat from the global economy."

So, in varying degrees, would all the states. The conference highlighted the extent to which every state's economy has become internationalized as world trade has increased sevenfold since 1970.

Forty-nine states sponsor export seminars, and 25 offer export finance programs to meet the needs of local companies.

Gov. Lamar Alexander (R-Tenn.) has made eight trade missions to Japan in seven years, and his state has received 10 percent of all Japanese investment in the United States. Japan-bashing does not stir the same juices there as in Pittsburgh or Detroit.

Alexander says he thinks that the party that frames the trade issue in terms of improving the nation's "competitiveness" will come out ahead. He cited General Motor Corp.'s plan to cut into Japan's price advantage on small cars by overhauling management practices and union-contract provisions at the Saturn plant to be built in his state.

The Democratic governors also are taking cracks at the "competitiveness" theme, but most have noticed that the gut-level appeals -- about job loss and unfair competition -- get the applause.

"It used to be a subject that made people's eyes glaze over," said Arkansas Gov. Bill Clinton (D). "Now when you talk about it, audiences don't just listen, they actually perk up."

The only trick is figuring out what to say.