Norfolk & Western Railway tripled its third-quarter earnings and will have its most profitable year ever, Chairman John R. Fishwick said yesterday.

The railroad's profits jumped to $39.4 million ($1.26 a share) from $13.2 million (42 cents) a year ago, when a coal miners' strike slashed business. Norfolk & Western revenues jumped from a strike-depressed $141.3 million to $364.5 million.

For the first nine months of 1979, N&W has earned more profit than it made in all of 1976, the railroad's best year ever, Fishwick told a meeting of securities analysts in New York.

The nine-month earnings total $140.2 million ($4.49) compared with $69.1 million ($2.21) in the same period a year ago and well above the $4.21-a-share record set in 1976, Fishwich said. The railroad earned $5.29 a share in 1978, but $1.90 of that came from a special credit.

Smithfield Foods Corp. said its third-quarter earnings climbed to $837,000 (35 cents a share) from $543,000 (22 cents) in 1978. Sales increased to $42.6 million from $38.7 million.

For the first nine months, however, Smithfield earnings are lagging at $1.72 million (72 cents) compared with operating earnings of $2.66 million ($1.06) a year ago. Sale of a restaurant subsidiary produced nine-month net last year of $5.38 million ($2.15).