Pan American World Airways and Eastern Airlines reported sharp drops in third-quarter profits yesterday, due largely to rising fuel costs, but Allegheny Airlines said its profits reached a record high.

"We're doing a better job," said Edwin I. Colodny, Allegheny's chairman and president, after the airline said earnings were $12.7 million (98 cents a share), up from $11.9 million ($1.45) in the same quarter of 1978. Revenues were $195.2 million, up from 153.3 million.

Eastern reported earnings of $3 million (7 cents a share), down 85 percent from $20 million (93 cents) in the same quarter last year. Revenues rose from $605 million to $730 million.

Pan Am said it earned $60.8 million (86 cents a share) during the quarter down from $101.3 million ($2.01) in the same quarter last year. Revenues rose 10.5 percent to $742.8 million.

Allegheny's "third-quarter results from operations are encouraging as they were produced despite continually rising fuel and other costs," Colodny said. "October traffic and advance reservation for the holiday season are also strong."

"Our strong traffic growth did offset some of the cost-escalation impact," said Eastern Chairman Frank Borman.

"Our fuel bill for the first nine months of 1979 had already surpassed the total for all of last year," said Charles J. Simons, Eastern vice chairman and vice president. He said the airline has spent $464.1 million so far this year for jet fuel compared with $428.2 million spent for all of 1978 and that the airline's fuel bill is up 45 percent, although the amount of fuel is up just 7 percent.

Pan Am said its cost of fuel rose 67 percent.

For the first nine months of this year, Eastern earned $42.4 million (1.54), off from last year's earnings of $63.7 million ($2.99) when 4.8 million fewer shares were outstanding.

Allegheny said it earned $24.3 million ($1.94) during the first nine months, down from $26.1 million ($3.77) in the previous year's period.

Pan Am said its nine-month earnings were $89.0 million ($1.25), down from $123.4 million ($2.71). Revenues rose 10.9 percent to $1.85 billion.

Colsolidated Edison Co. reported higher net income for the third quarter of 1979 at $118.1 million ($1.73 a share) on revenue of $937.1 million compared with net income of $104.3 million ($1.51) on revenue ot $800.6 million in the third quarter of 1978.

The third-quarter increase, however, brought earnings for the first nine months of 1979 slightly ahead of last year's nine-month figures at $254.3 million ($3.57) on revenue of $2.47 billion compared with $253.8 million ($3.57) on revenue of $2.30 billion.

Con Ed is the nation's seventh-largest utility.

National Steel Corp. reported record third-quarter sales, but said earnings were held down by rising costs.

Net income was $39.2 million ($2.03 a share) compared with $40.4 million ($2.10) during the same period in 1978. Revenues totaled $1.1 billion versus $965.7 million in the 1978 period.

National earned $105.2 million ($5.45) for the nine months compared with $74.3 million ($3.87) in the same period last year. Sales and other income amounted to $3.3 billion compared with $2.7 billion a year earlier.

Nation Chairman George Stinson blamed rising costs of energy, materials, and service and labor.

TRW Inc. reported a 10 percent increase in earnings and a 20 percent jump in sales for the third quarter compared with the same period of a year ago.

In the third quarter, earnings were $46.3 million ($1.25 a share) on sales of $1.1 billion compared with earnings of $42.2 million ($1.15) on sales of $928 million in the same 1978 period.

Nine-month earnings were $144.3 million ($3.91) on sales of $3.4 billion, up from earnings of $124.9 million ($3.40) on sales of $2.8 billion in the same period a year ago.

Textron Inc.'s third-quarter sales were up by 1 percent, but net income declined slightly from the comparable quarater last year, company Chairman Joseph B. Collinson said yesterday.

Third-quarter net income was $41 million ($1.09 a share) compared with $42 million ($1.11) in 1978's third quarter. Sales were $801 million compared with $795 million in the 1978 period.

In their first nine months, Textron earned $126.1 million ($3.35) compared with $122.8 million ($3.27) in the first three quarters of last year. Sales rose to $2.51 billion from $2.32 billion.

American Broadcasting Co.'s announced third-quarter net income of $31.9 million ($1.14 a share) from continuing operations on revenue of $463.6 million, both higher than the comparable quarter last year.

ABC said income from continuing operations in the 1978 third quarter, totaled $24.8 million (89 cents), excluding results from ABC Records, which subsequently was sold. Revenue amounted to $392.9 million.

For the first nine months of the year, ABC reported net imcome from continuing operations of $114.4 million ($4.08) compared with $87 million ($3.15) last year. The 1978 figures exclude results from ABC Records and ABC Record and Tape Sales Corp., which later were sold.

Nine-month revenues rose slightly, to $1.4 billion from $1.3 billion a year earlier.