The Soviet Union, hungry for hard currency, is reaping a windfall from higher oil prices and would like to increase exports to take advantage of shortages caused by the Middle East crisis. But it can't.

The problem is an antiquated and long mismanaged Soviet petroleum industry unable to boost production. It may, in fact, yield 500,000 fewer barrels a day this year than last, Western analysts say.

The Soviet Union produced about 12.1 million barrels of oil a day last year, one-sixth of the world's total and more than Saudi Arabia, Iraq and Kuwait combined.

It exported 3.7 million barrels a day -- more than Iraq -- with about half going to the West.

"They are producing at maximum capacity and their production is declining. There's no way they can get increased production," said John Lichtblau, chairman of the Petroleum Industry Research Foundation.

Not only is the Soviet industry unable to boost production, but also its problems with nuclear reactors have added to the domestic demand. The Soviet Union's appetite for oil is second only to the United States's.

"There's no way that they can take advantage of what's happening in the market," said Robert Ebel, vice president for international affairs for Enserch Corp., an engineering and construction company.

Ebel and other U.S. experts acknowledge that the Soviets are expected to gain hundreds of millions of dollars in additional hard currency in the coming months if the higher oil prices stand.

It's estimated that every $1 a barrel increase could mean $1 billion a year in additional hard currency for the Soviet economy. Last year, oil exports brought $20 billion in hard currency into the Soviet Union, accounting for about 40 percent of the country's hard currency earnings.

As oil prices began to climb after Iraq's invasion of Kuwait, Soviet oil bound for exports also became more valuable. A Moscow business publication, Kommersant, estimated recently that the worldwide jump in oil prices could increase Soviet hard currency revenue by $750 million by the end of the year.

Some Western analysts suggested the increase could be twice that.

If the Soviets export 1.3 million barrels a day to the West and prices continue to hover at $25 a barrel, compared with $16 a barrel before the Iraqi crisis, they stand to gain $1.5 billion in additional hard currency this year.

The Soviets also have said they want Eastern Bloc countries, where the other half of Soviet oil exports are sent, to begin paying in hard currency next year, according to U.S. oil experts.

But the Soviet windfall will be muted by declining production that also will force down exports. Production at its Mammoth field on the edge of Siberia reportedly has declined by one-fourth since 1988.

Based on performance over the first seven months of the year, the Soviets may average only 11.6 million barrels a day in 1990, compared with 12.1 million barrels a day in 1989.

"That's a rather dramatic drop," said Ebel, the Enserch executive and former U.S. intelligence expert. "For what they have to sell to the West, they're going to get more money. But the amount of oil is going to be less."

Soviet oil reserves are estimated to be more than 60 billion barrels, twice that of the United States. And the Soviets are wooing Western petroleum companies in the hope of expanding exploration and improving production facilities plagued by years of mismanagement, outdated equipment, deteriorating pipelines and a shortage of money for capital improvements.

In the past, the Soviets shied away from seeking out foreigners in developing its vast oil reserves. Even when oil prices were declining, the Soviet government poured large amounts of funds into oil development and boosted production. Revenue from oil exports pumped up other areas of the economy.

But the cost of exploration for Soviet oil has nearly tripled in the last five years and the Kremlin last year began to reduce funds for oil development.

It also stepped up its search for outside technical assistance and began negotiating possible joint exploratory ventures with Western oil companies.

Both Chevron Corp. and Texaco Corp. have reached preliminary agreements with the Soviets on joint oil exploratory ventures.

A number of U.S. service companies also are involved in oil exploration with the Soviets, as is Elf-Aquitaine, France's largest oil company.

The Soviet Union announced yesterday it has hired Wavetech Geophysical Inc. to help it open the country to competitive bidding for oil and gas exploration and production by Western companies.

"They want to get Western technology and capital," said Lichtblau of the New York-based Petroleum Industry Research Foundation.

But, he added, those new ventures are unlikely to have an impact on production for years to come.

"They desperately need American technology and American finances" to boost oil exploration and production, said Henry Shuler, a Soviet expert at the Center for Strategic and International Studies in Washington.

"About all they can hope to do in the short to medium terms is slow the rate {of oil production} decline."