Someone has come along to cover up the slogan, but if you look closely it is still visible, spray-painted on a wall behind Manama's gold market: "Down With the Khalifa Regime." On nearby walls are stenciled images of Iran's Ayatollah Ruhollah Khomeini.

The Bahraini government of Emir Isa Sulman Khalifa is trying 73 men on charges they sought to turn the slogan into reality and transform this progressive little principality on the Persian Gulf into an Iranian-style Islamic republic. Although the plotters were arrested before they could move, their enterprise has sent shivers through the gulf and intensified Arab support for Iraq in its drawn-out war to the north against Khomeini's forces.

The challenge to Bahrain's rulers put a spotlight on a broad threat to the security of the gulf region. It stems not only from Soviet--or even Iranian--troops but also from the appeal of a Shiite Moslem revolution against the established Sunnite order and the danger posed by what diplomats and gulf officials say is an active Iranian program to promote Shiite subversion among Arab neighbors.

"It is not only Bahrain," said the Bahraini foreign minister, Sheik Mohammed Mubarak Khalifa, in an interview. "You have other nationalities involved. I think everybody sympathizes with us. It is no longer just a Bahrain affair. It is a gulf affair."

Bahraini authorities said 13 of those arrested were Saudi citizens. Another was from Oman, they said, still another from Kuwait and the rest were Bahrainis. Perhaps more importantly, all were Shiites and, the authorities charge, nearly all had received military training in Iranian camps across the gulf.

Bahraini investigators have accused Iran of providing the plotters, members of the Islamic Front for the Liberation of Bahrain, with equipment ranging from radios to Israeli-made Uzi submachine guns--and even fake Bahraini police uniforms whose buttons had "made in Iran" stamped on the back.

In addition, informants here said, some of the group's leaders have indicated in interrogation since their arrest last December that they were led to expect support from Iranian planes or Hovercraft if their coup attempt met strong opposition.

"There are certain Iranian policies and they come from the very top," the foreign minister said. "Let us be clear about that."

Bahrain ordered Iran's charge d'affaires in Manama to leave the country, saying he used his diplomatic pouch to import walkie-talkies from London that were destined for the arms cache found in a $120,000 safe house bought by an accused plotter last fall.

Although Bahraini and diplomatic sources describe the Iranian threat as gulf-wide, this little island midway down the western coast presents a particularly opportune target. Like Iraq, its population of about 260,000 Bahrainis contains a Shiite majority, some of Iranian ancestry, ruled by a Sunnite group, the Khalifa family.

Bahrain's prosperity and enlightened leadership has meant there are virtually no poor Bahrainis. But the distinction between the island's Sunnites and Shiites is burdened with social and political meaning as well as religious doctrine.

The ruler and his Cabinet total 17. Five are Shiites, all in technocratic ministries such as health and transportation. The Khalifa family took over Bahrain 200 years ago, after coming from farther south on the gulf, and established its dominion on an island then populated mainly by Arab Shiite fishermen and date growers.

"The original Shiites here all think they have had their birthright stolen by the Khalifas," said one diplomatic observer.

Against this background, the Iranian revolution in 1979 and the Shiite disturbances in neighboring Saudi Arabia in November of that year stirred considerable interest here. The idea of Shiite revolution became the focus for opposition to the ruling family, replacing several leftist groups including Nasserites and Communists.

Riots in Saudi Arabia's eastern province and sedition in Iraq demonstrated Iran's effect there as well. Bahrain and Iraq are the only gulf Arab countries with Shiite majorities and the Saudi Shiite minority is small. Gulf officials and diplomats here express fears, however, that an Iranian-style revolution could nevertheless threaten other states, even among Sunnites, if it succeeded in one through a mixture of Islamic fervor and anti-monarchical and leftist ideology.

In the meantime, however, the appeal of Iran's revolutionary call has dropped off as gulf Arabs watch the war with Iraq and troubles in Iran where, as one Bahraini official said, "Those people they are shooting are not Sunnites--they are Shiites."

"The Iranian revolution is no longer a model for anybody," said Bahraini Information Minister Tariq Abdul Rahman Moayyed. "Three years ago, when it just began, of course it looked nice. But now. . . ." His voice trailed off, then he added: "The export of the revolution from Iran is really no longer a problem, that is, the export of ideals. But the export of subversion, yes, that is a problem."

The prime minister, Sheik Khalifa Sulman Khalifa, the prince's brother, nevertheless has ordered a tightening of restrictions on practices forbidden by Islam. In a country with a long liberal tradition, however, the tightening has changed life only slightly, Arab residents here report. Alcoholic drinks are still freely available, for example, and Bahraini as well as foreign women often dress in Western styles.

But security concerns have increased sharply since the coup plot was discovered. The prince used to move about his island accompanied only by his driver. His host at a recent dinner said he arrived with two security vehicles in front and two behind, all four filled with Bedouin guards recruited from Jordan.

Bahrain and its partners in the regional Gulf Cooperation Council also have stepped up exchanges of internal security information, diplomats report. Arab sources said the discovery of several Bahraini plotters in the nearby United Arab Emirates--reportedly after arrival of a flight from Beirut--led to the uncovering of the would-be coup here.

The council, comprising Bahrain, Saudi Arabia, Kuwait, Qatar, Oman and the United Arab Emirates, was formed last year as a security pact with strong backing from the United States.

Saudi security officials have participated in interrogating the prisoners in Bahrain, diplomats here report, and the Saudi interior minister, Prince Nayef, charged that Iranian-backed agitators are aiming at Saudi Arabia as well, part of a broad group called the Islamic Front for the Liberation of the Gulf.

"There are training camps in Iran where substantial numbers of gulf Arabs are being trained in martial arts, and presumably not just because it's a pleasant pastime," a Western diplomat said.