Lured by soaring oil prices, prodded by the International Monetary Fund, and threatened by international lenders. Mexico has edged its way into the ranks of the energy exporters and into what President Carter hopes will be a growing robe as a supplier to the United States.

Expectations about potential imports from Mexico have risen dramatically since 1974 when the Central Intelligence Agency classified bullish estimates of Mexican oil finds "Top Secret," and Mexico's president then, Luis Echeverria, was, as a senior State Department official said, "confronting the U.S. in every Third World forum possible."

It is a different story now.

Energy Secretary James R. Schlesinger and others say the United States will be importing 2 billion cublic feet of natural gas a day from Mexocm hopes to be exporting by then. Mexico's exports are now 200,000 barrels a day and could rise later in the '80s to 2 million barrels a day, they say. Elsewhere U.S. energy officials admit the United States may enter into a direct purchase agreement with Petroleous Mexicanos (Pemex), the state oil company, to buy oil for Carter's 1-billion-barrel strategic petroleum reserve. CIA analysts in the meantime mull over projections that Mexico could export up to 4.5 million barrels a day - most of it aimed at the U.S. market.

U.S. Ambassador to Mexico Patrick Lucey is equally optimistic. "Mexico in the near future will be a very significant factor in the world energy market," he says.

The key to rising expectations about Mexican oil and natural gas exports is signs that newly elected Mexican President Jose Lopez Portillo is repersing the direction of his predecessor's energy and economic policies - to say nothing of his strident rhetoric. These changes, in part, have been dictated by Portillo's efforts to meet the conditions of an agreement his government negotiated with the International Monetary Fund last year to improve Mexico's credit-worthiness and reduce the country's mounting balance-of-payments deficit.

U.S. officials admit there is a link between Mexico's new aggressiveness to develop energy exports under Portillo and economic realities, typified by the IMF agreement.

"The Mexican government recognized they could improve their credit-worthiness through oil and gas exports," says Cecil Thompson, who was assistant administrator for international affairs of the former Federal Energy Administration. Yesterday, the FEA and the Federal Power Commission were folded into the new Department of Energy.

Asked if the United States pressured Mexico into exporting oil and natural gas another official said. "If there is a conspiracy to get them to develop their oil and gas, it is a conspiracy of the market saying we're not going to invest our money unless you improve your economic situation."

Over the past year and a half, the international banking such as Chase Manhattan, Bank of America, and First National City Bank of New York - became increasingly concerned about Mexico's ability to service its mounting foreign debt. Last year it was above $25 billion - almost the highest of the developing countries - $13 billion of which was held by U.S. banks.

Because of a deteriorating trade balance, lagging domestic economic growth, and a 30 per cent inflation rate. Mexico devalued its peso, unhinging it from the dollar for the first time in 23 years.

At the urging of the United States, the banks, and the Treasury Department. Mexico entered into a stabilization agreement with the IMF last fall. In return for emergency credits, Mexico agreed to strict limits on wages,increases in its money supply, and a $3 billion ceiling on new borrowing this year. One expert called it "a classic, fiscally conservative, balance-of-payments document." In short, an austerity program.

Portillo, the first finance minister to become president in Mexico's history, had a major hand in negotiating the IMF agreement, and was quick to change Mexico's energy posture and court foreign investment. Weeks after his inauguration Portillo upgraded Mexico's official proven oil reserves from 6.3 billion to 11 billion barrels, and launched an ambitious $15.5 billion oil development plan.

He also has made changes in Pemex, which was created when Mexico nationalized the American-dominated oil industry in 1938. (The extreme sensitivity to foreign participation in oil in Mexican politics is tied in part to a stinging trade embargo President Roosevelt imposed on Mexico in retaliation for the expropriations.) Portillo has brought the independent agency under control of a cabinet-level group that dictates policy. One international oil expert said. "He is no longer running it like a utility."

American oil firms such as Dallas based Halliburtion Co. and Odeco, Inc., have stepped up activities in the oilboom southern states of Mexico.

Earlier this year, Pemex began intensive negotiations with a group of six American natural gas pipeline companies led by Texas Eastern Transmission Corp. and Tenneco, Inc., to sell 2 billion cubic feet of gas a day from the massive Reforma Field in Chiapas and Tabasco, two states along Mexico's eastern coast. The companies signed a letter of intent Aug. 4, and have since filed an import license request with the Federal Power Commission. Other companies have begun talks to buy gas piped 300 miles north from new fields discovered in Baja California along Mexico's Pacific coast.

"We're talking about a lot of gas, it is a very important project," says Charles Curtis, former FPC chairman and now head of the Federal Energy Regulatory Commission, an autonomous section of the new Department of Energy. The gas will account for about 3 per cent of total U.S. consumption when it starts flowing at full capacity upon completion of the 850-mile, $1.5 billion pipeline in 1979.

To expedite the project, the Export-Import Bank has sent Congress two proposals to give Pemex $400 million in credits and cash to finance U.S. purchases for the pepeline construction, and an additional $338 million to buy $500 million in oil development equipment from U.S. suppliers.

One sticking point so far is the price.

Pemex and the companies are going to ask the FPC to approve a price tied to the energy equivalent of imported heating oil - now about $2.60 per thousand cubic feet. This is well above the $1.75 Carter asked for in his natural energy plan. More important, it is more than the $2.16 per thousand cubic feet America pays for Canadian imported gas.

State Department Latin America expert Richard Arellano says, "The Mexicans are shrewd businessmen and canny negotiators, driving as hard a bargain as they can - they will also find out there are market limits."

One thing that is certain is that the price Mexico intends to ask for its energy resources will be at the world market level, now set by the 13-member Organization of Petroleum Exporting Countries. The gas price Pemex is asking for, for example, is near the price Algeria and Indonesia, both OPEC members, are asking for liquified natural gas, and the United States is already buying oil from Mexico, as it did recently for the strategic petroleum reserve, at OPEC prices.

U.S. officials point out that Mexico has learned to benefit from OPEC's pricing policy without joining the organization. Thus far Mexico has shown little interest in entering OPEC, in part because it would lose trade advantages with the United States. One White House official summed it up, "No matter who they sell the oil to, it will help us."

The larger question in Mexico's future as an exporter - barring a return to Echeverria's policies - is the size of Mexico's oil reserves. One axiom in international oil circles is that official reserve figures are political and economic-as well as geological - statements.

Pemex's head, Diaz Serrano, said last March that Mexico's total energy resources are well above the 60-billion-barrel figure used by some governement officials as "probable reserves." If Mexico has that much oil, it would be on a par with Kuwait and Iran, OPEC's second largest producer.

DeGolyer and MacNaughten, a Dallas firm noted for accuracy in reserve estimates, has been hired by Pemex. So far the results are encouraging. But industry sources stress that more extensive drilling is necessary before the figure can be taken seriously.

Most international specialists, however, are still skeptical about projections above the 40-billion-barrel mark. More than a few point to similar optimistic projections coming from Indonesia in the '60s, generated to attract foreign investment, credit, and political favor. While Indonesia is now an oil exporter, it failed to fulfill earlier promises.

One investment banker whose firm has long experience in Latin Americal says, "The numbers being bandied about are put out to appease the international financial community - they are floating them to get financing."

While uncertainty lingers whether Mexico is another Iran, one thing is clear - the Mexican oil boom is on. Mexico has gas and oil, andU.S. banks, energy companies and consumers want a piece of it. CAPTION: Illustration, no caption, By Ray [WORD ILLEGIBLE] for The Washington Post