No one's an outcast at the global weapons bazaar.

Countries with little in common, or even on opposing sides of alliances, come together in the arms trade, whether they do so openly, under the table or -- as in the case of an intercepted missile shipment from North Korea to Yemen -- hidden amid a cargo of cement.

With all but the most advanced weapons, arms experts say, if you've got the cash, you can get what you want.

And their only surprise when the transaction between North Korea and Yemen was uncovered was that the United States did something to stop it.

"They say politics makes strange bedfellows," said Jon Wolfsthal, an authority on nonproliferation at the Carnegie Endowment for International Peace. "The international arms trade is no different."

U.S. officials decided Wednesday to let the unflagged cargo ship carrying the Scud missiles sail on its way to Yemen after concluding they had no legal basis to seize the shipment. Intelligence officials shadowed the ship for weeks and the Spanish navy stopped it Monday off the Arabian peninsula.

North Korea is an ambitious exporter of ballistic missiles, but not alone in offering its military wares to practically all comers.

The U.S. government has warned for several years about leapfrogging advances in missile technology throughout the developing world. More small countries, using equipment and expertise from Russia, China and North Korea, are no longer just customers, but weapons exporters in their own right.

The breakup of the Soviet Union also has spawned smaller but sizable arms-exporting enterprises that are hard to control. Among them, Belarus has become one of the world's largest arms exporters -- a country with a hardline leadership and close ties to Iraq and other states accused of trying to amass highly destructive weapons.

In a small example of conventional-arms proliferation repeated many times over, a particularly effective German assault rifle is being manufactured in perhaps 17 countries -- most with far less stringent export controls than the major suppliers face, experts say.

And the two shoulder-fired missiles that narrowly missed an Israeli airliner recently were the old -- but still highly effective -- Soviet SA-7 missiles, versions of which are being made in half a dozen countries or more, said Edward Laurance, author of "The International Arms Trade."

"God only knows where all those things are," he said.

Some reasons there are more players in the arms trade: licensing agreements that let one country's weapon be produced in another; readily available technical information and the spread of reverse engineering -- taking something apart, figuring out how it works and coming up with a way to make it.

Wolfsthal said almost any country able to make cars can also make tanks and other sophisticated military hardware.

North Koreans "have the incredible ability to reverse-engineer anything they get their hands on," he said. "The Chinese are taking Russian airplanes and making their own production lines. The Iranians have bought not only ballistic missiles from North Korea but a production capability."

The United States is the largest arms merchant by far, delivering almost half the weapons bought on the world market. America netted $14 billion from arms exports in 2000, more than double the earnings of its closest competitor, Britain, with Russia in third.

Like other top arms suppliers, the United States does not sell directly to hostile nations -- except in shady deals like the arms-for-hostages arrangement with Iran in the 1980s.

But this is an amorphous world of shifting relations and military hand-me-downs.

One result: U.S. forces faced U.S. Stinger missiles in Afghanistan, leftovers from the arms supplied to the Afghan resistance in its war against the Soviet Union.

Another: Iraq invaded Kuwait in 1990 with weapons bought from all major arms powers, including the United States.

And another: In perhaps the last chance to avoid another Iraq war, inspectors are searching there for evidence of weapons of mass destruction, including chemical weapons that Saddam Hussein once used against Iran -- when U.S. officials sided with him.

"In the past 20 years, Pakistan was our friend, then our enemy, friend, enemy, friend," Wolfsthal said. "Alliances change quickly."

North Korea has been selling industriously to anyone who wants to buy.

U.S. allies such as Egypt and Pakistan have bought from North Korea, experts say, and so has Iran. President Bush branded North Korea, Iran and Iraq an "axis of evil" because of their existing or potential arsenals of the world's worst weapons.

Yemen is part ally, part trouble spot for the United States -- its backcountry seething with anti-American militancy but its leadership cooperating with the United States in the war against terrorism.