Mexico has warned OPEC that while it is maintaining its present oil prices and export cutbacks through the end of January, it may soon "reconsider" these price-propping measures if the cartel fails to "reestablish effective discipline" in enforcing price levels and production quotas.

Criticizing the "destablizing trading practices" of other unnamed oil exporters, Mexican officials declared in a statement released last night that Mexico could be forced to alter its own oil marketing policies "to protect its international commercial position."

The statement marked Mexico's first public display of displeasure with the Organization of Petroleum Exporting Countries, with which it has collaborated for more than a year in price and export policies.

For the past two months, Mexico voluntarily has reduced its crude sales by about 6 percent, exporting an average 1.44 million barrels daily, down from the 1.54 million barrels per day averaged from January to October. Mexico also has resisted pressure to slash prices, keeping its top-grade Isthmus blend -- comparable in quality to OPEC's Arabian light -- at $29 per barrel, equal to the marker price set officially for the OPEC oil.

Mexico will continue for at least another month to charge its present prices and to restrict exports by approximately 100,000 barrels daily, the government announced here last night following a meeting of its Cabinet-level oil-marketing committee.

The self-imposed export cut costs Mexico $83 million monthly in lost revenues, while a dollar-per-barrel oil price drop would reduce Mexico's foreign exchange earnings by $48 million monthly. "It is better to try to defend price levels even if we temporarily sacrifice the total volume of crude exports," President Miguel de la Madrid said last week.

De la Madrid said that Mexico, like the leading OPEC nations, had ruled out the alternative of boosting export volumes because "increasing exports could provoke a price drop, with the net result of this additional exporting effort being that our income stays the same or declines."

Exporting an average 1.53 million barrels of oil per day, half of it to the United States, Mexico will collect about $15.1 billion from oil sales in 1984, nearly 70 percent of its total export income. Mexico is the United States' leading foreign oil supplier.

Among exporters not affiliated with OPEC, Mexico is surpassed in importance only by the Soviet Union. Mexico recently criticized the Soviets for their failure to cooperate with OPEC's price-supporting production restraints.

Although Mexico consistently has refused invitations to join OPEC, it has worked closely with the cartel to brake the continuing slide of oil prices, attending OPEC meetings as an observer and honoring the cartel's price and production guidelines. OPEC officials have applauded Mexico's "exemplary solidarity," contrasting it with their view of the more market-oriented conduct of such other non-OPEC exporters as Britain and Norway.

Mexican officials complain, however, that many OPEC members undercut the official cartel price structure through swap agreements and discount sales in the Rotterdam-based spot oil market. "Pemex does not sell crude on the spot market . . . or participate in barter operations," the government's statement asserted, referring to the Mexican state oil company.

"Mexico cannot remain indifferent to the lack of discipline by OPEC's member countries," said the statement, adding that "if other producers do not act responsibly, our country will have to reconsider its present oil export policies."

Unlike most non-OPEC producers, Mexico could increase its export levels substantially, many industry analysts believe.

Since 1982, Mexico has adhered closely to its official export ceiling of 1.5 million barrels per day. OPEC officials and independent specialists estimate that Mexico now has the capacity to boost exports by more than 200,000 barrels per day.