VIENNA, DEC. 12 -- Oil ministers of the 13-member Organization of Petroleum Exporting Countries reached the brink of agreement today to extend their existing price and production pact, but industry analysts said that the expected accord would not be sufficient to keep oil prices from dropping on world markets in coming weeks.

The expected price decline could knock a nickel or more a gallon off the cost of gasoline and heating oil early next year, according to U.S. oil industry specialists observing the conference here.

It also would make it easier for the United States and other oil importing countries to cope with potential economic difficulties from October's stock market crash. U.S. oil-producing states would suffer, however.

The OPEC ministers failed in four days of bargaining at their semiannual conference to adopt a significant reduction in total OPEC production, delegates said.

A cut of about 5 percent is believed to be necessary to stabilize prices and halt current overproduction.

Oil traders who have predicted a decline in prices have been monitoring negotiations in recent weeks to see whether OPEC would move to curb overproduction.

Instead, OPEC was close to agreement on maintaining its overall production ceiling of about 15 million barrels a day for all of its members except Iraq, the ministers of Ecuador and Gabon said.

The official price will remain at $18 a barrel, they said, despite repeated demands from Iran for a price increase.

The ministers had yet to agree on how long OPEC would maintain its current pricing structure, Ecuadoran minister Fernando Santos said.

Some ministers wanted to consult their home governments overnight, he said.

Some delegates said the meeting was expected to end Sunday.

"I think that with this agreement, {the price per barrel} could easily fall by $1.50 to $2" within a week, said Michael Rothman, a senior energy analyst for Merrill Lynch Capital Markets.

Without an agreement, prices could drop even more sharply, he and other analysts said.

A confrontation between Iran and Arab oil-producing states in the Persian Gulf, led by Saudi Arabia, was at the heart of the disagreements that prevented a more far-reaching agreement.

Iranian Petroleum Minister Qolam Reza Aqazadeh-Khol and his Saudi counterpart, Hisham Nazer, reportedly did not speak directly to each other during the first three days of the conference.

Principal mediators between the factions were the oil ministers of Nigeria, Venezuela and Indonesia.

Both Iran and Iraq, enemies in the seven-year-old Persian Gulf war, are pressing for measures that would help them increase their oil revenues, which both countries use to finance military expenditures.

At this meeting, Saudi Arabia and Kuwait sought Iraq's return to the OPEC fold, after an 18-month-hiatus in which Baghdad has ignored OPEC-mandated ceilings on its production.

Iraq has demanded that OPEC raise its production quota to the same level as Iran.

Iran has said that it would boycott any accord granting Iraq such parity.

Barring a surprise, Iran will win that battle here, and Iraq will continue producing at about double its current 1.5 million barrel-a-day ceiling.

"I think there will be agreement among 12" of the 13, Santos, the Ecuadoran oil minister, said.

But Iran lost in its effort to raise oil prices by at least $2 a barrel. It drew support on that issue only from Libya, and the Saudis were particularly determined to block any price hike, largely because market conditions would not support such a move.

The dispute was mostly for public consumption.

While repeatedly demanding a price increase, the Iranians themselves have been offering discounts for their oil of between $1.50 and $2.50 a barrel in order to find buyers in recent weeks.

The wrangling over prices and Iraq's quota diverted OPEC efforts from reaching substantive agreement on production cuts, so the conference moved simply to extend its current ceiling.

While the official OPEC production ceiling is 16.6 million barrels a day, members are producing between 18 million and 19 million barrels a day because of Iraq's nonparticipation and cheating by some other states.

OPEC would have to reduce its actual production to less than 17 million barrels a day in order to stabilize prices, U.S. markets experts say.

"A roll-over {of the existing agreement} will mean that real production will be between 18 {million} and 18.5 million barrels a day. That's at least one million barrels a day over demand in the first quarter," Bryan Jacoboski, an oil analyst for the investment brokerage firm, Paine Webber Inc., said.

"Prices {of crude oil} will come down one or two dollars {a barrel} rather quickly" under the expected accord, Jacoboski said.

He said that, in turn, could mean a cut in U.S. gasoline and heating oil prices of five cents, and possibly more, a gallon before spring.

Another U.S. oil expert, who insisted on remaining unidentified, was somewhat more cautious. He said crude prices would drop by several dollars "only if OPEC members continue to overproduce."

But he added, "I don't see anything new" in the expected agreement.