The local cartoonists have been having a field day with the "second conquest" of Mexico. One showed a group of conquistadors with gas cans rushing up to an Indian under an oil rig, shouting "Amigo!" Another had a buxom Mexican woman on Uncle Sam's lap, as he whispered in her ear: "I'm not after your money -- there are other values as well."

The cartoonists, of course, are right. Mexico's spectacular new oil reserves have caused a sensation and led to are-discovery of this country, to modify the cartoonists' view.

The wave of would-be customers from Europe, Japan and Latin American prompted Mexican oil chief Jorge Diaz Serrano to exclaim recently, "We are frankly as inundated with buyers as with oil."

Members of OPEC, the international oil cartel, have once again started to drop heavy hints, hoping to get the obstinate Mexicans to join their club.

But above all is a flurry of official reports and press accounts in the United States -- which is suddenly feeling vulnerable in its energy supply by the turmoil in Iran -- that bluntly ask: "What's in it for us?"

Mexico's firm retort so far has, "First of all, what's in it for Mexico?" And by all appearances, this. may remain the Mexican administration's position for the remaining four years of its term.

Pemex, the state oil monopoly, has signed all of its crude export contracts for 1979, committed most of its 1980 production and drawn up production goals through 1982 that it is calling "rational." Whatever the changes in the geopolitics of energy, President Jose Lopez Portillo emphasized in an interview this week that he was determined to abide by these plans.

That decision, he said, was a combination of the country's ability to absorb the new income without distorting the economy and the oil industry's own capacity to expand without relying wholly on foreign equipment.

A cautious administrator who shifted the economy from crisis to near recovery and cut inflation in half -- down to 17 percent -- in two years, Lopez Portillo has frequently pointed at financial mismanagement in other oil producing nations. He regards avoiding congestion and rampant inflation as determining factors in Mexico's short- and medium-term oil strategy.

But in addition, the oil industry itself, according to oil chief Diaz Serrano, is bound by strict political and technical rules. Mexico's goal is to export petrochemicals rather than endless quantities of crude. And although the industry has recently grown at unprecedented rhythms -- it virtually doubled its production to the current 1.5 million barrels per day in two years time -- Diaz Serrano maintains that "we could not grow much faster than planned even if we wanted to."

A rare hint of obstacles to growth -- Pemex has always been extremely discreet about internal operations -- surment and of construction materials," as well as "problems resulting from land expropriations which led peasants in the oil regions to set up road-blocks and to occupy the land."

But regardless of the political or economic restraints Mexico's energy picture is impressively rosy.

Suspecting that there are oil and gas faced in a report released last week. It said that almost 8 percent of Pemex's 1978 budget had not been spent because of "a shortage of drilling equipdeposits under most of Mexico's territory, Pemex is feverishly exploring now in 27 of Mexico's 31 states and in large areas of the Gulf of Mexico.

The country's proved reserves -- 11 billion barrels two years ago -- have burgeoned; two weeks ago they were set at 40 billion barrels, with estimated additional reserves at 4.6 billion barrels above that. Mexico's potential reserves remain at 200 billion barrels, far exceding any other country in the western hemisphere. At current production rates Mexico's 40 billion barrels are sufficient to last the country 60 years.

However, predictions made recently that Mexico could fill 30 percent of U.S. import needs by the mid-1980s are being contradicted by Lopez Portillo and his staff.

Mexico's production targets are much lower. While 85 percent of Mexican oil exports last year went to the U.S., with the remaining 15 percent was shared by Israel and Spain, Mexico's "export diversification plan" called for a cutback in the U.S. proportion of total exports of crude.

Pemex export director Juan Aizpura said that this year, for example, 80 percent of Mexican crude will go the U.S., while by 1980 the U.S. share will be down to between 60 and 66 percent with the balance going to Europe and Japan.

But because Mexico's total exports will increase rapidly -- they should reach 1 million barrels per day, double today's rates, by 1980 -- the U.S. will not receive less but somewhat more Mexican oil.

That Mexico's nationalism is a force to be reckoned with became clear one year ago when the Mexican oil chief and U.S. energy secretary James Schlesinger clashed over Mexican natural gas sales in Washington. Diaz Serrano stormed out of Schlesinger's office after what a Mexican diplomat described as "unbelievable arrogance and insults from Schelesinger." The result was that Mexico decided to use its gas surplus domestically -- and lose money -- rather than accept the lower U.S. price.

Early last year, the U.S. Ambassador to Mexico was reportedly laughed at in the Department of Energy when he reported that much of Mexico's industry was switching from oil to natural gas as a source of energy. But the domestic gas pipeline feeding that industry will be inaugurated on March 18.

"Schlesinger was very important in raising our consciousness about not trusting the U.S. and carrying out our own plan," said a high Mexican official. "He not realize it but he did us a favor in the end."

As Mexico steps up its oil production, however, additional vast quantities of gas will become available and they are known to be of interest to the U.S. The Mexican president has said he is willing to sell these "if the conditions are right." Lopez Portillo said he expects to discuss this with President Carter during his visit to Mexico in mid-February.

But referring to Schlesinger's statement this week that it is not in the interest of the U.S. to buy Mexican gas, an irritated Lopez Portillo said once again the U.S. was being "erratic."

"I know what to do with my gas. I'll use it at home and I'll sell it at a price that suits me," he said. "If they (the Americans) don't want to discuss it, that's it: We just won't deal with the matter."