Southern Railway yesterday reported record profits for 1976 despite a decline in fourth-quater earnings, which chairman and Navy Sectretary-designate W. Graham Claytor Jr. attributed to increased spending for maintenance.

Norfolk & Western Railway and the Union Pacific Corp., meanwhile, also reported record 1976 profits. Southern N&W and UP traditionally are among the most profitable of the country's rail companies.

Washington-based Southern's profits last year totaled $89.24 million ($5.85 a share), up 14 per cent from $78.33 million ($5.12) in 1975 and 1.3 per cent above the previous record of $88.1 million earned in 1974. Revenues climbed 19 per cent to $1.03 billion.

In the final quarter, Southern's profits fell 7.8 per cent to $24.6 million $1.61) compared with $26.7 million ($1.77) in the 1975 period as revenues rose by nearly 12 per cent to $270 million.

Clayton, recently nominated by President Carter to be Secretary of the Navy, said the fourth-quarter dip reflected a 20.6 per cent boost in maintenance of ways pending and a 35 per cent increase in equipment maintenance over the 1975 period.

All major commodities groups contributed to the gains last year, rainging from a 7 per cent increase in food peoducts to a 47.5 per cent rise in transportation equipment, including autos and parts. Directors approved a regular quarterly dividend of 58 cents a share on common stock, payable March 15 to stockholders of record Feb. 15.

Union Pacific earned $187.7 million (4.02 a share) in 1976, a gain of 26 per cent from $148.6 million ($3.21) the previous year as revenues rose 15 per cent to $2.02 billion.

Not included in the 1976 earnings above was a one-time gain of $7.5 million (16 cents) which brought total net income for the year to $195.2 million. Chairman Frank E. Barnett said this gain resulted from lower costs than were anticipated for UP's transfer of passenger operations to Amtrak in 1971.

In the fourth quarter, UP earned $58 million (2.47 before the one-time gain vs. $44.7 million ($1.93) in 1975. Barnett said fourth-quater transportation profits were slightly ahead of the 1975 period but that the rate of growth slowed toward the end of the year. Non-transportation profits were up sharply, he said.

Norfolk & Western listed record full-year and fourth-quarter profits but said cold weather this month has caused added expenses and lost business. With coal frozen in some cars, coal unloadings at Norfolk are off 20 per cent, for example.

Roanoke-based N&W said fourth-quarter profits totaled $45.6 million ($1.49 a share) a gain of 19 per cent from $39 million ($1.25) in the same period last year, the previous record for any quater. Revenues were up 11 per cent to $314 million.

Profits for the full year rose 50 per cent to $131.5 million (4.21) compared with $87.5 million (2.80) in 1975. Revenues increased 16 per cent to a record $1.22 billion.