Sears, Roebuck and Co., parent of the largest U.S. retailer, said yesterday that second-quarter earnings totaled $284.9 million, a 7.3 percent increase over the same period last year, on record quarterly sales of $10.75 billion.

The company said second-quarter earnings came to 77 cents a share, compared with earnings of $265.5 million (72 cents a share) on sales of $9.84 billion in the 1985 second quarter.

For the first six months of this year, earnings totaled $480.2 million ($1.29), compared with $488.8 million ($1.32) for the same period last year. Revenue was up 8.3 percent to $20.14 billion from $18.6 billion a year ago, the company said.McDonald's Corp., of Oak Brook, Ill., yesterday reported record net income, revenue and sales for the quarter and the six months ended June 30.

For the quarter, McDonald's earned $129.8 million ($1.01 a share) up 10.8 percent from last year's $117.1 million (90 cents). Total revenue was up 12 percent to $1.07 billion from $955.5 million a year ago.

For the first six months, McDonald's net income increased 11.2 percent to $223.9 million from $201.4 million. Per-share earnings increased from $1.54 to $1.73. General Motors Acceptance Corp. said it earned $298.6 million for the second quarter of 1986, up 25 percent from $238.9 million a year ago, primarily because of a record amount of new vehicles financed.

For the first half of the year, the credit and financing arm of General Motors Corp. posted a net income of $575.2 million, up 23.6 percent from $465.2 million in the first half of 1985. PepsiCo Inc., citing the significant impact of a one-time gain on 1985 results, yesterday reported earnings in the second quarter declined to $121 million (47 cents a share), compared with $256 million (89 cents) in the year-ago quarter.

For the first half of 1986, earnings totaled $189 million (73 cents), compared with $319 million ($1.11) last year. Mobil Corp., the nation's second-largest oil company, reported yesterday that because of certain nonrecurring gains, its second-quarter earnings were 42 percent higher than in the same period a year ago.

Mobil said it earned $582 million ($1.42 a share), compared with $411 million ($1.01) in the second quarter of 1985. Revenue totaled $12.2 billion, down from $14.3 billion a year ago. For the first six months, Mobil's earnings advanced 40 percent to $1.02 billion ($2.50 a share) from $731 million ($1.79) in the first half last year. Revenues were off 11 percent to $26.1 million against $29.4 billion. Ashland Oil Inc. said its quarterly profit was up 33 percent, including a record net income from operations. Ashland, based in Ashland, Ky., said it earned $80.2 million ($2.36 a share), compared with $60.3 million ($1.79) in the three months ended June 30 -- the third quarter of Ashland's fiscal year. Quarterly sales totaled $1.8 billion, down from $2.1 billion last year.

Ashland's nine-month earnings rose to $168 million ($4.93 a share) from 100 million ($2.74) in the year-earlier period. Sales declined to $5.6 billion from $6 billion. Weirton Steel Corp., the nation's largest employe-owned company, said it earned $10 million on sales of $277.9 million in the second quarter of 1986. First-quarter earnings in 1985 were $8.9 million on sales of $289.6 million, the West Virginia company said. Shipments and selling prices this year lagged behind those of mid-1985.