Mexico has some of the best-oiled machinery in the world -- literally.

Latest estimates of its combined petroleum and natural gas reserves (proven, probable and potential) are put at 250 billion barrels. Of this figure, 60.1 billion barrels are proven reserves and 38 billion are probably reserves. Roughly two-thirds of the reserves are oil.

Mexico's growing collectionss of gushers enabled it to rebound dramatically from its worst recession in 40 years in the late 1970s and ride out the current world economic slump with a 1980 growth rate of 8 percent, the same as in 1979.

But it also has become apparent, especially in recent months, that no amount of lubrication can compensate for the rustiness and inefficiency of some mechanisms in the Mexican economy. In fact the faster the machine is driven the more conspicuous and painful these short-comings become.

Inflation, now estimated to reach 30 percent or more this year, is the result.

Mexico is rapidly increasing the level of its imports, reducing trade barriers and importing inflation with all the new merchandise.

Thanks mainly to its oil export revenues, expected to be something more than $11 billion this year as compared with $3.8 billion last year, Mexico's balance of trade deficit through June was 25 percent lower than for the same period in 1979.

But it was still $887 million.

More than 60 percent of Mexico's imports come from the United States, which has had plenty of rising prices to export.But another 20 percent of Mexico's imports come from such inflation-wracked nations as Great Britian, Italy, Spain, Brazil and even Argentina, where inflation tops 100 percent.

Domestic pressures put even higher pressure on prices, however, as President Jose Lopez Portillo indicated in his state of the nation address Sept. 1.

One of the most serious problems for the Mexican economy comes under the general heading of bottlenecks. The country's ports and railroads, decrepit antiques that languished for decades, are incapable of handling the sudden surge in trade. As a result, sometimes vital shipments of everything from food to drilling equipment are held up for months.

The Lopez Portillo administration, in the fourth of its alotted six years, having successfully guided the country out of the chaotic economic situation it inherited in 1976, is now trying to consolidate its gains.

Mexico's oil revenues have had the effect of artificially propping up what is increasingly viewed as an overvalued currency. Mexican manufactured goods are being priced out of the world market. Effectively pegged to the dollar, the peso has hovered at an exchange rate of between 22 and 23 since it was allowed to plunge by about 45 percent at the end of the last president's administration.

In any case, no one believes such a drastic move would be necessary or sensible this time around.

The government is also reviewing its extensive subsidy program. Subsidies have risen at an annual rate of 39 percent over the last 10 years and in 1980 accounted for 51.7 percent of the government's direct budget outlays.

Although Lopez Portillo has just given government workers a wage increase of as much as 27 percent, the majority of Mexico's work force has seen a steady deterioration of its buying power -- and there was not much of that to begin with.

In fact, the problem of underemployment, linked with the problem of the unemployable, is perhaps Mexico's most serious problem.