BAGHDAD, IRAQ, OCT. 19 -- The Iraqi government announced a rationing system for gasoline and engine oil today, citing shortages of chemical additives because of the U.N. blockade imposed to force President Saddam Hussein's troops out of Kuwait.

The measure, in a country with huge oil reserves and a major petroleum industry, was the clearest indication to date of disruption caused by the economic embargo authorized by the U.N. Security Council after Iraq seized Kuwait on Aug. 2.

Baghdad motorists and taxi drivers immediately formed lines at service stations, seeking to fill their tanks before the rationing system is put into effect.

An announcement from the Oil Ministry said rationing cards for private cars, taxis and trucks should be picked up beginning Saturday at distribution centers listed in the press and that the cards will be necessary to buy gasoline or oil beginning Tuesday.

Basic foodstuffs -- including tea, bread, rice and milk -- have been rationed since early last month. But the addition of gasoline was expected to have a particular impact here and abroad because petroleum is the symbol of Iraq's rise as a modern economic power, accounting for 90 percent of government revenues before the Persian Gulf crisis.

Apparently with the local reaction in mind, the government announced the measure on Friday, the Moslem day of prayer and rest, when commercial activity was at its lowest and the ordinary rush of traffic slowed to a weekend pace.

Abroad, however, the step is likely to be read as a sign the embargo has begun to take hold in Iraqi industry, which diplomats here have said is the key target.

Although gasoline has remained plentiful at a government-set price equivalent to slightly more than $1 a gallon at the official exchange rate, engine oil has been scarce for the last several weeks, with prices climbing steadily and taxi drivers lining up at distribution points to buy supplies.

Oil Minister Issam Abdul-Rahim Chalabi said that although exports have been blocked, Iraq is pumping enough oil to meet domestic consumption of between 300,000 and 400,000 barrels a day.

"The only reason for this {rationing} is to guarantee that we will have the additives and chemicals that we require to continue making these products," he told reporters. "We are only rationing gasoline and lubricants because they depend on additives that we have to get from the outside."

These would include, for example, lead, oxidation inhibitors and metal deactivators in gasoline and additives to prevent engine wear and deposit buildup in crankcase oil, according to oil industry sources.

Gasoline prices will remain the same, Chalabi said, but the amount allocated to different categories of drivers has not yet been established.

Asked whether the shortages are likely to affect Iraqi's million-man military establishment as well, he smiled and responded: "I think you'll understand these things have been taken into consideration, and we will have to ensure we supply these requirements."

A major producer in the Organization of Petroleum Exporting Countries, Iraq was exporting about 2.8 million barrels a day before the gulf crisis. But under the U.N. embargo, virtually no exports are leaving the country, depriving the government of its main income source while prices skyrocket on the world market.

"That must be driving them crazy, to see the oil sheiks on the other side stuffing their pockets full of money because of the price rises, while they are getting nothing," a foreign businessman commented.

In what was interpreted as an effort to force down prices, Chalabi announced Thursday that Iraq will sell oil to anybody for $21 a barrel, including U.S. companies, providing the buyers can pick it up on their own.

The Iraqi minister predicted some countries will be tempted by the Iraqi offer because, despite Saudi Arabia's production increases, the West is likely to face oil shortages of about 2 million barrels a day as winter weather begins to bite in the next few weeks.

The $21 price was set by OPEC ministers in Geneva last July as a compromise between Iraqi demands for higher levels and Saudi efforts to keep prices down.

Before its invasion of Kuwait, Iraq charged that Kuwait was driving prices down by producing above its agreed quota.

Thursday's offer, however, appeared nearly meaningless in practice. Tankers would not be allowed to break the U.N. embargo, which is being rigorously enforced by U.S. and allied warships in and around the Persian Gulf. Saudi Arabia and Turkey have closed Iraqi pipelines through their territory to ports on the Red Sea and the Mediterranean.

Chalabi argued that oil sales at $21 would not violate the U.N. embargo because Iraq would agree to have payments deposited in foreign financial institutions pending resolution of the gulf crisis.

"It is their business to get the necessary approvals," he explained. "They will have to argue that this is not in violation of the embargo, because Iraq is not getting a single penny."

In any case, Chalabi indicated that the underlying Iraqi motive was to get prices down, depriving Saudi Arabia and other oil countries of the extra revenue piling up because of price rises attributed to the gulf crisis.

"We will be happy to see the price go down, even if we don't sell any oil," he added. "The consumer will benefit, and we will be happy." Prices dropped about $2 a barrel today, to about $34.70.

The minister also said Iraq has begun supplying Jordan with all its oil needs, 60,000 barrels a day. Previously, Iraq supplied about 40 percent of Jordan's needs, largely by truck. Saudi Arabia provided about half and Jordan made up the small difference through foreign purchases and its own tiny production.

Saudi Arabia announced Sept. 19, however, that it would no longer provide oil to Jordan. Riyadh cited arrears in payments, but the cutoff was interpreted in Jordan as retaliation for King Hussein's sympathetic stand toward Saddam.

In other developments, the State Department said today that Iraq had allowed six more Americans to leave. The six, four of whom were pulled off a charter flight leaving Iraq last week, arrived in Amman on Thursday, Reuter reported.

A report published in Iraqi newspapers today said all foreigners in Kuwait must register with local authorities before Nov. 5. Those who fail to do so "will be responsible before the law," the report said.

In Ottawa, the External Affairs Department announced that its last five diplomats in Kuwait have abandoned Canada's embassy there and have arrived in Baghdad.

External Affairs Minister Joe Clark said the embassy was not being officially closed, only that operations were suspended, according to Reuter.

"It is no longer feasible for them to remain given available supplies, which are nearing exhaustion, and to stay would jeopardize their health," Clark said in a statement.

Only a few foreign missions, including those of the United States and Britain, remain operating in defiance of Saddam's order for the closure of all embassies in Kuwait.