Never mind about the Panama Canal, Taiwan and SALT II. Congress is on the brink of a Star Wars-style treaty fight that the pact's critics are portraying as a potential Armageddon for the American free enterprise system in outer space.

At issue is an obscure "moon treaty" negotiated under United Nations auspices to safeguard and develop the resources of space as the "common heritage of mankind."

Leading the fight against it is an equally obscure group of prospective space colonists and their armchair boosters who see the treaty, with all its terrestrial power-politics implications, as an obstacle to their free-spirited expoloration of the heavens.

So futuristic and even otherworldy were the origins of the struggle that official Washington paid scant attention until the space people did a very worldly thing.

They hired a high-powered Washington lobbyist named Leigh S. Ratiner, who cut his lobbying teeth for the Kennecott Copper Corp. on the Law of the Seas negotiations, and then let nature take its course.

Ratiner has wrapped his cause in the American flag, warning that the treaty would "doom free enterprise initiative in outer space" and subjugate American interests to those of developing Third World nations.

"The American people will not want to give up the hopes and aspirations for America's future in space -- their sense of national achievement and accomplishment," he told a House Science subcommittee recently.

Ratiner's crusade has jangled nerves at the State Department which defends the treaty as an improvement on existing international rules. Officials say it simply establishes fair-play rules for resource exploitation, including "orderly and safe development . . . rational management . . . . and equitable sharing by all [nations] in the benefits derived from these parties." Any restrictions on free enterprise expolitation date back to a 1967 treaty, they argue.

"You can still make a buck off the moon, if there's a buck to be made there," said an exasperated State Department aide.

But Ratiner argues that the practical effect of the treaty would be a "moratorium on private-enterprise space exploitation, and "control" by collectivist Third World countries at the expense of industrialized societies. This has set off some tremors on Capitol Hill.

In the House, several members are circulating a resolution opposing the treaty.

Even stronger rumbles are coming out of the Senate, which would have to approve the pact. Leaders of the Foreign Relations Committee, including Chairman Frank Church (D-Idaho), are considering asking the Carter administration to hold off signing the treaty and to seek revision of some controversial provisions.

Space-oriented industries have yet to be heard from, but they may be soon. Ratiner flew to the West Coast late last week to round up aerospace industry support for the campaign against the treaty. After meeting with industry representatives, he said he received no commitments but was "encouraged."

A grass-roots space campaign also is sprouting. Letters are beginning to pour in to legislative offices, and an advance guard of about 20 space enthusiasts is expected to begin prowling the halls of Congress this week.

The group that Ratiner represents is called the L-5 Society, formed at a 1975 Princeton conference on space manufacturing facilities and named for an Earth-orbit location that is considered well-suited for human colonization. Its board of directors includes scientists, authors, engineers and Sen. Barry Goldwater (R-aiz.).

"For those of us who plan to go into space, it's a give-me-liberty-or-give-me-death kind of issue," said Carolyn Henson of Tucson, Ariz, a founder of the 3,500-member society and its outgoing president.

While Ratiner has stressed the national security and technological aspects of the treaty fight. Henson said many supporters are also "Timothy Leary and Whole Earth Catalogue people who are more interested in social experimentation than the technological side."

Said Henson: "we're the new pioneers."

For all its Daniel boone, Horatio Alger and Buck Rogers connotations, the dispute nevertheless involves serious questions - global haves vs. havenots, technology tranfsfer among nations, the potential for resource development in space.

As of now, the resource potential appaears to be about as fertile as one's imagination, judging from literature on the subject. Atiner holds out the lure of "major industrial activities which could produce substantial portions of the world's energy requirement," including a solar-power satellite to convert the sun's energy for use on Earth within 15 to 20 years.

Whether the treaty would encourage or discourage such developments is central to the dispute.

Proponents argue that its restrictions on expolitatin are minimal and fill a void that might otherwise attract "more hair-raising schemes," as a State Department offical put it. Opponents like Ratiner contend the treaty mandates further negotiations leading to tighter restrictions and chilling exploration in the meantime. The State Department responds that the United States would be required only to negotiate, not to sign, any further agreements.

Congressional sources said skepticism about the moon treaty is deepened in some quarters by dissatisfaction with Third World demands in the troubled U.N. seabed negotiations. Ratiner is no longer lobbying for Kennecott on that issue but cites the controversy as analogous. State Department officials say the United States is better protected in the moon treaty.

The treaty -- officially the draft Agreement Governing the Activities of States on the Moon and Other Celestial Bodies -- is expected to clear the U.N. General Assembly shortly for signing by member nations. As of now the United States, which has participated in seven years of negotiations on it, is expected to cosponsor the agreement, State Department officials said.