Enron Corp., the nation's largest natural gas transmission company, said Thursday it was considering the sale of its oil and gas subsidiary, one of the biggest U.S. independent oil and gas concerns. ``Based upon prices paid in recent transactions for oil and gas reserves, the sale of all or part of EOG (Enron Oil & Gas Co.) would strengthen substantially Enron's financial position and provide the flexibility to pursue very attractive opportunities we see in the energy business,'' said Kenneth L. Lay, Enron chairman. Enron Oil & Gas had reserves of 1.42 trillion cubic feet of natural gas and 42.3 million barrels of oil as of the end of 1987. For the entire year, it sold an average of 343 million cubic feet of natural gas and 12,000 barrels of oil per day. For the first three months of 1988, that rate has risen to 399 million cubic feet of gas and 13,000 barrels of oil, the company said. ``Assuming completion of a sale, we will be realizing for our shareholders the tremendous value inherent in these assets under current favorable market conditions,'' Lay said. He said proceeds from a sale would be used to reduce Enron's indebtedness and interest expense and enhance near-term earnings and future cash flow. Lay, speaking at Enron's annual meeting Thursday, said debt reduction was a major goal for 1988. Debt as a percentage of capitalization stood at 75.6 at the end of 1987 and was reduced to 67 percent by the end of the first quarter. Enron earlier Thursday reported first-quarter earnings of $69.4 million, or $1.20 per share, compared with $62.7 million, or $1.06 per share, for the year-earlier period. ``Among the primary causes was a return to more normal winter temperature patterns than the relatively warm heating seasons of the last three years,'' Lay said. ``The colder weather, resulting in increased natural gas use, was coupled with higher average prices for gas, which also proved beneficial to earnings.'' In releasing the financial figures, the company restated earnings for 1987 to reflect adoption of changed accounting rules, reducing 1987's reported first quarter earnings by $3.9 million, reflecting a lower federal income tax benefit due to a tax rate change relative to depreciation and amortization expenses.