UAL Inc., parent of United Airlines, lost $40.3 million in the first quarter because of worsening economic conditions and rising jet fuel prices and will skip its regular quarterly dividend on common stock, the company said yesterday.

The loss followed 1979's loss of $72.8 million, which the company attributed to a prolonged strike that shut down United Airlines, the nation's largest transportation company.

Delta Airlines also reported lower profits yesterday for its third quarter, but Texas International Airlines posted higher first-quarter earnings.

Ual's directors declared the regular quarterly dividends on the company's preferred stock, but decided to omit common-stock dividends for the first time in six years.

The first-quarter loss, equivalent to $1.37 a share, came despite a 19 percent increase in revenues to $1.16 billion from $973 million in the same period a year ago.

UAL Chairman Edward E. Carlson said jet fuel costs have nearly doubled in the last year.

"We think our shareholders are better served by making sure the company has the cash to build a fleet of airplanes that's fuel-efficient and fully cost-competitive," he said.

UAL will pay dividends of $1.375 a share on its 5 1/2 percent cumulative prior preferred stock and 10 cents a share on Series A preferred stock.

Delta Air Lines' third-quarter net income fell to $21.8 million ($1.10 a share) from $26.197 million ($1.32) in the same period of 1979 as revenues increased from $597.3 million to $769.1 million.

Nine-month net income also dropped to $55.49 million ($2.79) from $93.01 million ($4.68) as revenues rose from $1.75 billion to $2.14 billion.

Texas International Airlines said its first-quarter net income was $1.5 million (22 cents a share) compared with $548,000 (8 cents) a year ago. Revenues rose from $47 million to $72.5 million.

Procter & Gamble Inc., a food and household products giant, reported a 12 perfect gain in earnings for its third fiscal quarter on a 14 percent rise in sales.

Net income was $189.19 million ($2.29 a share) on sales of $2.79 billion compared with $168.98 million ($2.04) a year on sales of $2.45 billion.

For nine months, P&G earned $521.53 million ($6.31), up 13 percent from $462.99 million ($5.60) a year earlier. Sales rose 16 percent to $8.076 billion from $6.992 billion. Chairman Edward G. Harness said that unit volume was up a little but the gains were mainly the result of price boosts.

Lockheed Corp. reported first-quarter earnings of $12 million (67 cents a share fully diluted), down slightly from $12.4 million (72 cents) in the same 1979 period. Sales rose from $1 billion in the 1979 first quarter to $1.1 billion.

Lockheed Chairman Roy Anderson said improved aircraft program profits for the first quarter had been offset by higher interest expenses.

Program profits, excluding the L-1011 TriStar and other income, interest and income taxes, were $75 million compared with $66.9 million in the first quarter of 1979. Interest expenses were $29.7 million compared with $14.6 million in the first quarter of 1979.

TriStar program losses were $26.6 million compared with a $35.9 million loss in the first-quarter of 1979.

Two companies that supply oil-exploration concerns also reported increased earnings.

Schlumberger Ltd., a global oilfield supply firm, said it earned $1.50 a share in the first quarter, up from $1.01 a year ago, as sales soared to $1.61 billion from $572.01 million.

Net .income was $191.01 million against $128.06 million.

Acf iNdustries Inc., a diversified manufacturer, earned $1.82 a share in the first quarter, up from $1.31, largely on improved sales of oilfield and railway equipment.

The gains were made despite a sharp drop in the company's automotive components business.

Net income was $16.14 million on sales of $268.82 million compared with $11.44 million a year ago on sales of $251.98 million.

The 1980 profit included a capital gain of 31 cents a share on the sale of a half interest in the Carter-Weber Carburetor subsidiary of the Weber interests.