The love-hate fandango between the United States and Puerto Rico could not get much more tangle-footed than it is right now.

A collection of the island's best and brightest, spokesman for nearly all of its political splinters, spent three days closeted at the Wilson Center in the Smithsonian Institution this week, arguing about the commonwealths' future.

They emerged with most of their preconceived notions intact. There was agreement, however, about a few things:

It was three days of "pessimism, dissatisfaction, divisiveness and lack of direction," said private researcher Luis Davila, to general acclaim.

The United States has no idea whatever about what is going on in Puerto Rico, but had better learn pretty quickly. The participants seemed united only when they ganged up on Carter administration officials for what political commentator Juan Manuel Garcia Passalacqua called "selective inattention" to Puerto Rican problems.

The current commonwealth relationship with the United States is crumbling both politically and economically and cannot be saved, and a new structure has yet to emerge. "In the interregnum, a lot of morbid symptoms appear," said Passalacqua.

As with most things in Puerto Rico, the debate roiled around whether the island should seek to become the 51st state of the union, declare itself independent or refashion the commonwealth into something more coherent.

Carter administration delegates, speaking for background and not for quotation, told the islanders that they had only to agree among themselves and America would gladly try to provide what was wanted.

President Carter and most of his presidential challenges have promised to abide by the results of a plebiscite, probably in 1981. Until then, one Carterite said, America's interest in the island is neither economic nor traditional, but primarily historical. "The American people probably won't focus on this issue until they have to," he said.

He added that he hoped it would not prove as difficult an issue as the Panama Canal treaties.

This drew muffled hoots and catcalls later on. "That is totally an attitude of 'We're innocent bystanders,'" said Federico Hernandez Denton, a law professor and former pro-commonwealth government cabinet member.

The administration, he and others complained, forgets that the 3 million Puerto Ricans are all U.S. citizens. Only Cuban Premier Fidel Castro's yearly attempt to have the United Nations condemn U.S. colonialism keeps American diplomats awake on the issue, they said.

Yet President Nixon's intelligence operatives had set out to weaken pro-independence forces in the early 1970s, and President Ford plumped for statehood against the advice of his own advisory commission, several participants recalled.

With $4 billion in food stamps supporting 65 percent of the islanders now, America's stake in Puerto Rico is already large. With independence would come chaos for the 1 million Puerto Ricans now living on the mainland. With statehood would come political upheaval in the form of 3 million Spanish-speaking voters and seven new members of Congress, probably all Democrats.

"We have to bring people who think they aren't affected by Puerto Rico's future to realize that they are affected," said Miami Mayor Maurice Ferre, who is Puerto Rican.

Any plebiscite will be challenged unless it is decisive in getting something more than a bare majority of votes for one viewpoint, a U.S. official said. Just how much more remains an issue.

Indepedent observers like the United Nations or the Organization of American States should perhaps supervise all aspects of the plebiscite to make it credible in an area where vote fraud charges are routine, several participants suggested.

Although independence forces have not mustered more than 6 percent in any election since 1960, Cuba and other Third-World countries barely realize there are alternatives, one U.S. adviser said.

"Those who don't support independence have to be more active in explaining your case, particularly to Latin Americans," he warned. "They write the Third-World position . . . and any hope of legitimacy for statehood or commonwealth must come from them."

Statehood forces insist that the United States would have to assume the island's internal debt, that income and other federal taxes would be imposed only over a 20-to 25-year transition period, and that Spanish language and culture in the schools must not be disturbed.

Hernandez condemned that as "ghetto statehood," while statehood backers admitted there had to be more talk about whether statehood would be desirable even if the U.S. Senate balked at these conditions.

There was no talk of the violence that independence backers have promised if they do not get their way. "We thought it wise not to go into it," said Passalacqua, "because it's what we're trying to prevent."