Croatian officials are studying powders found on board a ship bound from Yugoslavia to Iraq to see whether the Iraqis could use them to improve the performance of Scud missiles, Croatian police officials said today.

At least four containers on the ship Boka Star contained the suspicious powders, according to officials at the Adriatic Sea port of Rijeka. They declined to give further details, awaiting additional study. "We will have to wait and see," said a police official by telephone.

The cargo had been described as spare parts for MiG-21 fighter jets, which are Soviet-designed planes dating from the 1950s that are part of the remnants of Iraqi President Saddam Hussein's air force. A Croatian official in Rijeka told the Reuters news agency that inspectors had found no jet parts aboard the ship.

Croatian officials seized the Boka Star on Tuesday after it left the port of Bar in Montenegro, one of the last two remaining republics of Yugoslavia. The ship flew a Tonga flag of convenience, although the crew was Montenegrin.

A Western official, while declining to offer details about what was found on the Boka Star, said that investigators would try to discover whether the powders might have been produced from formulas used in a defunct Yugoslav rocket program.

The interception of the ship followed a NATO military raid on Oct. 12 on the Orao institute arms factory in the Serb-controlled zone of Bosnia. Documents seized at the plant linked the factory with weapons exports to Iraq.

Although the factory is located in Bosnia, it has links with the Jugoimport, a state-run Yugoslav weapons production firm with several factories in Serbia, the dominant republic of Yugoslavia. The factories produce light and heavy weapons, ammunition and explosives.

The State Department spokesman, Richard Boucher, said there was "clear evidence" that both Orao and Jugoimport were refitting Iraqi military jets. Weapons sales to Iraq are forbidden by a U.N. embargo.

In advance of a possible U.S. invasion of Iraq, sales of military equipment to the country are a red flag for the Bush administration. U.S. reports say that Iraq possesses at least two dozen Scud missiles left over from the Persian Gulf War. During the war, Iraqi troops fired 93 Scuds at Israel and Persian Gulf allies of the United States.

In response to complaints by the U.S. Embassy in Belgrade, Yugoslav President Vojislav Kostunica dismissed Jugoimport's director, Jovan Cekovic. On Thursday, Kostunica sacked three other officials linked with the alleged sales to Iraq: the director of Orao, Milan Prica, the head of the Air Force, Miljan Vlacic, and Spasoje Orasanin, who runs the government's weapons sales office.

Iraq is not a new customer for Yugoslavia. The Arab country bought $2 billion of arms in the 1980s when it was at war with Iran. In the 1990s, Yugoslavia developed close trade ties with Iraq when both countries were under U.N. trade and arms embargoes.

Kostunica tried to play down the scandal. It "only boils down to overhauling older-generation aircraft engines, rather than selling state-of-the-art weapons," he told reporters Thursday. He said that Jugoimport was active in breaking a U.N. embargo on Yugoslavia during the 1990s, and it was "mean and hypocritical" for anyone to be "almost offended" because the company continued its old ways.

"This affair, too, has been used as a pretext to launch fresh attacks against the federal authorities, the Yugoslav army and me personally," he said.

Jugoimport was once part of the integrated Yugoslav army weapons industry, but former president Slobodan Milosevic converted it into a state-run holding company for diverse industries that included weaponry, construction, food processing and pharmaceuticals. Milosevic is now on trial at the U.N. war crimes tribunal at The Hague.

Cekovic, the ousted Jugoimport director, denied involvement in arms trafficking with Iraq. He said the document at Orao suggesting a Jugoimport connection was "planted."