Sliding oil means slick footing for next Mexico head. Mexico's President-elect takes office next month with a weak political base. Falling oil prices could further add to his woes.

Just as Mexico seemed to be creeping out of its economic crisis, plunging world oil prices have sent the country reeling again. The loss of an estimated $2.5 billion in oil revenues this year could not have come at a more sensitive political moment. On Dec. 1, President-elect Carlos Salinas de Gortari will take office with the support of just one-quarter of all eligible voters, the weakest position for an incoming president in modern Mexican history.

Economists and political analysts here say the squeeze on oil revenues could jeopardize the new leader's primary mission and political salvation: the success of a government freeze program intended to control inflation and eventually spur an economic reactivation.

Washington, showing support for Mr. Salinas, helped cover the initial erosion in revenues by offering a $3.5 billion loan in October. The package is expected to tide the new administration over its first weeks.

But economists here warn that without more loans and permanent foreign investments, the drop in oil prices will cause deeper damage to the economy - and the people.

They say it will sap the country's foreign reserves, further strangle public spending, and threaten the so-called Economic Solidarity Pact - a wage, price, and exchange-rate freeze that has lowered inflation from 15.5 percent a month in January to less than 1 percent in October.

``The current drop in prices is an extremely grave threat to Mexico,'' says Mario Ram'on Beteta, who directed the state oil monopoly, Petr'oleos Mexicanos (Pemex), during the oil-price collapse of 1986. (For instance, the price per barrel of Isthmus 33 grade oil fell from $13.20 to $11.62 in the last week of October.) ``It reduces the inflow of foreign currency. It reduces Pemex's capacity as a taxpayer. And even as nonoil exports have grown, oil revenues continue having a heavy influence on public finances.''

Even today, as the government tries to wean Mexico from its dependence on oil, Pemex is the real muscle of the economy. It accounts for more than a third of state revenue, a quarter of government spending, and nearly 40 percent of Mexico's export earnings. It is the United States' key oil supplier, shipping in 36 percent of the US's strategic reserve and selling 50 percent of its oil exports to US companies.

But Pemex's huge income is dropping.

The government's 1988 budget had planned for an average price of about $15 a barrel. Oil analysts say it will end up about $10 a barrel, meaning a direct loss of nearly $2.5 billion this year.

``It's a catastrophe that presents an obstacle to the plans of Salinas and his government,'' one academic analyst says. ``The fall forces them to spend less on a budget that is already cut to the bone.''

The steep drop in revenues could jeopardize Mexico's anti-inflationary program in several ways.

``It's inflationary because it forces the government to finance public expenditures internally,'' says Fausto Alzati, a leading oil analyst. He says the gap in income will likely be filled by a new issue of Treasury bonds, which tend to push up interest rates and thus inflation.

By pushing Mexico's balance of payments into the red, it also eats away at international reserves, which provide an important cushion for the exchange rate, a pool for paying off the $104 billion debt, and the basis for a favorable investment climate.

Reserves hit a record $16 billion in the first half of the year. By September, the level had dropped to $11 billion, because of speculation and gradually declining oil prices. After the latest dive in prices - one highly reliable source says it has fallen to $8.6 billion - and keeps on falling.

But the ominous clouds also have a silver lining.

Some economists say the oil-price woes gave Mexico the leverage to ask the US for the $3.5 billion loan - and will likely help it get a larger package early next year. There are strong rumors in government circles that Japan and several other countries will soon buoy the economy by making major capital investments here.