The secular government of Iraq is imposing strict security measures on the Shiite religious majority to guard against an Islamic revolution while at the same time sprucing up mosques in a bid to win Shiite loyalty.

The secret police continues to arrest and execute members of the Shiite Dawa Party on charges of planning urban guerrilla attacks, according to Iraqi government officials. Dawa seeks to promote a religious upheaval similar to the one in neighboring Iran, but the number of its bombings has dropped sharply since a major clampdown that included mass deportations of Shiites in 1979 and 1980.

Iranian radio broadcasts regularly urge Iraqi Shiites to rebel, and Iran's Army is seeking to invade Iraq and bring it the revolution by force in the two nations' 26-month-old war. Such a change would seriously threaten the stability of Saudi Arabia and other pro-Western Persian Gulf Arab oil states, but Western and Asian diplomats report that the Iraqi government appears to be strong enough to contain any unrest unless Iran wins militarily.

The Iraqi government, dominated by members of the Sunni rather than the Shiite branch of Islam, also is trying to buy the Shiites' support by renovating their shrines and providing them with improved social services.

New Italian marble tiles, funded by the government and President Saddam Hussein personally, brighten the courtyard around the gold-domed mosque here housing the tomb of the prophet Mohammed's cousin and son-in-law, Ali. Shiites in particular revere the shrine, because they believe that religious authority has passed down a line of succession going back to Ali and his son Hussein. Iran's Shiite leader, Ayatollah Ruhollah Khomeini, prayed at the mosque daily during 14 years that he spent in exile here.

Police cars abounded, and plainclothes security guards were easy to spot tailing reporters during a visit by U.S. correspondents to Najaf and two shrines at nearby Karbala. Iraqi officials said that precautions were necessary because of the presence of outsiders and because the visit took place on a Friday, the Moslem holy day, when Dawa attacks are most likely.

"They Dawa members have tried to cause trouble not only here but all over Iraq. Our security measures are quite good, and they have not achieved their goals," said Adnan Dawoud Salman. governor of the province of Karbala.

Membership in Dawa, which means "the call," is punishable by execution. Dawa guerrillas were known for hurling grenades into crowds during religious ceremonies, and attacks claimed by the party were frequent until the middle of 1980.

Iraq accused Iran of bearing much responsibility for the spate of terrorism, and the series of attacks fueled tensions that helped lead to the war.

Diplomats say the secret police have succeeded in infiltrating the party and arresting many militants. Baghdad residents say there has not been a major terrorist attack since August, when a car loaded with explosives drove into the lobby of the Planning Ministry and blew up, killing or wounding dozens.

The crackdown three years ago included deportation of tens of thousands of persons of Persian, Shiite origin. Conservative estimates say that 40,000 people have been forced to leave the country in the past five years, while some responsible sources say that the number is well over 100,000.

"A truck would come to a family's home, take the people and their belongings to the Iranian border and deposit them," a Western diplomat said. "Anybody who tried to help was arrested. We understand that it still happens occasionally."

The Iraqis say that all of the deportees were Iranian nationals, but diplomats say that they know of many with Iraqi identity cards forced to leave. Iran is demanding the repatriation of the deportees to Iraq as one condition for peace.

It is unclear whether Shiite unrest has declined only because of government repression. Some observers believe that the Shiites have been frightened by the excesses of Khomeini's government and that they identify themselves more as Arabs fighting the Persian enemy, Iran, than as Shiites opposed to Sunni, secular rule.

Iraq's ruling Arab Baath Socialist Party is trying to build a secular society and keeps Shiite clerics on a tight leash. In contrast to Iran, alcoholic beverages are sold freely and many women wear Western dress. Diplomats stationed here report the arrest of several dissident clergymen, adding that a few are believed to have been executed.

Shiite clerics in dark robes and cylindrical hats at the shrines at Najaf and Karbala made a point of praising the government -- expressing thanks for purchases of chandeliers, new tiles and central air conditioning for the mosques.

"All of this is to show you that the president and leadership really are concentrating on these holy places," Raouf Ahmed, second in charge at the tomb of Hussein in Karbala, told reporters. The cleanup effort began after the start of the war, when the government was particularly in need of Shiite loyalty. Shiites form the bulk of the infantry, and the government was afraid that a fifth column might emerge at home, according to diplomatic and business sources in the capital.

Shiite Arabs make up at least 55 percent of Iraq's population of 14 million, and some estimates say that their share has risen to 60 percent because of their relatively high birth rate. The rest of the populace, in descending order of size, is made up of Sunni Arabs, Kurds and a small Christian community.

The government has been careful to include the Shiites in its ambitious development plans. The provincial governor in Najaf boasted of a $200 million cement project and several 400-bed hospitals built recently. New water, sewage and electricity facilities have been constructed in the poor Shiite district in the capital of Baghdad that previously was called Al Thawra but now has been renamed Saddam City in honor of the president.

Iraq gave Khomeini refuge at Najaf until 1978 to keep a thorn in the side of the former shah Mohammad Reza Pahlavi, who then was a major Iraqi rival as the ayatollah is today. Khomeini went to France after being expelled as too incendiary a guest when tensions mounted with the shah, and the patriotic-sounding Shiite clergyman said they would not like him to return.