ANKARA, TURKEY, AUG. 7 -- The U.N.-mandated boycott of Iraqi oil products began to tighten into a stranglehold today as Turkey announced it would halt transshipments of oil from the Mediterranean end of twin Iraqi pipelines. Iraq itself cut by 75 percent the flow of oil through a pipeline across Saudi Arabia, apparently for lack of customers.

Taken together, the 810-mile-long Turkish pipelines and the 940-mile-long Saudi line have a normal daily capacity of more than 2.3 million barrels of oil, or about 85 percent of Iraq's total production. All other Iraqi oil exports -- and any oil from occupied Kuwait that Iraq might attempt to sell on world markets -- must traverse the narrow waters of the Persian Gulf and could be subject to an international naval blockade.

The Turkish announcement came as governments around the world conferred on procedures for complying with the trade boycott ordered Monday by the U.N. Security Council. If fully enforced, it could cripple the cash-strapped nation, which depends heavily on oil exports for economic survival. Together, Iraqi and Kuwaiti oil output totals about 9 percent of world daily production.

On Monday, Iraq cut off the flow of oil through one of the Turkish pipelines as purchase contracts dried up, and Turkish officials said today that the flow through the other line would be permitted until oil storage tanks in Turkey's Iskenderun Bay fill up, a process they said would take about six days.

"Shutting the pipeline is in Iraq's hands," Turkish Oil Minister Mehmet Kececiler told reporters here today, "but when we stop loading {ships and storage tanks}, Iraq will have to shut the pipeline."

The Turkish action follows at least three telephone conversations between President Bush and Turkish Premier Turgut Ozal in recent days, and Secretary of State James A. Baker III is due in Ankara Thurday for further consultations with Turkish officials. The loss of oil-industry revenue to Turkey as a result of its move against Iraq -- estimated at more than $5 million daily -- is also expected to be a subject of the consultations, and Turkish officials said they may seek some Western compensation.

Asked in an interview Monday with ABC-News anchor Peter Jennings if Turkey expected financial aid from the West, Ozal replied: "I believe that the most important thing is that we should stop this aggression. That is much more important" than compensation.

Meanwhile, at Saudi Arabia's Red Sea port of Yanbu, terminus of Iraq's other main pipeline, oil executives said the Iraqis had cut the flow of oil from about 800,000 barrels a day to about 200,000 and that storage facilities at the Muajjiz tank farm there were close to capacity for want of buyers.

It was not immediately clear if Saudi authorities would follow the Turkish example and allow the oil backup to force closure of the pipeline or if they would permit it to be loaded aboard ships.

Shipping sources in the region said the next scheduled loading at Muajjiz was to be Friday, when a tanker was due to take on a cargo of crude oil for India. It was also unclear if Iraqi oil purchased before the U.N. boycott vote and now in Turkish and Saudi storage tanks could be legally claimed by buyers.

Western diplomats in Ankara said the text of the Turkish statement cutting off oil exports was deliberately low-key to avoid antagonizing Iraq, with whom Turkey shares a 200-mile border. There are an estimated 30,000 Turks living in Iraq, and the Ankara government followed a policy of strict neutrality during Iraq's eight-year war with Iran.

About 5,000 U.S. military personnel are stationed in Turkey, a member of North Atlantic Treaty Alliance, but any proposal by Washington to use Turkey as a base for action against Iraq would require explicit approval from the Turkish government, a Foreign Ministry official said here today.

Turkey's armed forces total about 650,000 members, the largest in the Western alliance after the United States, and Washington will provide the Turks with about $515 million in aid this year, most of it in military hardware. Baker's visit here Thursday will underscore Washington's recognition of Turkey's continuing strategic importance despite relaxation of Cold War tensions and Washington's sensitivity to the risk Turkey has taken with today's action.

Turkey imports more than 50 percent of its oil for domestic use from Iraq, and moves were underway today to negotiate alternative sources. Some officials here said that in the meantime Turkey would feel free to draw on the hundreds of thousands of tons of oil still in the Iraqi pipelines to meet any urgent needs.

Osman Gedikoglou, general manager of the Turkish branch of the International Transport Association, estimated that 100,000 of Turkey's 300,000 truck drivers would have to seek new work if the U.N. sanctions remain in effect very long.

He said that most Turks nonetheless would support the government move, while hoping for some sort of financial mitigation. "We're wholeheartedly behind the decision," Gedikoglou said. "It's hard to say anything against it with everybody getting involved, but we will have to find a way for compensation."

No unusual military activity has been reported along the Turkish-Iraqi border, and there was little sense here that Turkey faced military retaliation from Baghdad for its action today. "They have enough problems without wanting to open another front, particularly one where they have troubles with the Kurdish minority," a Turkish official said.

When Iraq used poison gas against its rebellious Kurdish population in northwestern Iraq in 1988, some strayed across the Turkish border, and the Kurdish frontier region has been a focus of tension between the neighboring states ever since.

Turkish Oil Minister Kececiler said that under terms of the U.N. sanctions against Iraq, Turkey also had banned all trade with Iraq and Kuwait, apart from medicine and food needed for humanitarian purposes.

He did not make clear if Turkey would halt goods from third countries bound for Iraq through Turkish Mediterranean ports, but official sources said such a step was likely. Turkish trucks last year carried 1 million tons of imports to Iraq, most of it food.

The U.N. measure also bans all imports from Iraq and Kuwait and prohibits any activities, including the transfer of funds, that would help Iraq and occupied Kuwait export their goods.