Third-quarter operating income at Sea-Land Service Inc. grew 29 percent in the third quarter of 1992, the carrier's parent CSX Corp. announced Thursday.

Operating income expanded to $71 million from $55 million in the second quarter of 1992, the company said.The results show the effects of a major cost-cutting and efficiency drive at Sea-Land that began with the appointment of John Clancey as president and chief executive officer in 1991.

According to Sea-Land, the largest U.S. ocean carrier, with headquarters in Liberty Corner, N.J., the results of those efforts began to appear in the second quarter, when operating income was up 23 percent, to $54 million, from a year earlier.

The company has said it sees the efficiencies achieved so far as permanent changes in the way it does business, which will affect earnings well into the future.

"We anticipate a strong final quarter for 1993 as a result of (Sea-Land's) ongoing commitment to reduce the cost base and improve the returns of that business," said John Snow, chairman and chief executive of CSX. The company expects Sea-Land's 1993 earnings to exceed the $117 million earned last year.

Sea-Land's ratio of operating expense to revenue, called the operating ratio, declined to 91.6 percent from 93.2 percent in the second quarter of 1992, reflecting greater operating efficiency.

Operating revenue for the third quarter improved by $36 million, or 4 percent, to $846 million, driven by volume strength in the Pacific, Asia/ Middle East/Europe and domestic trade lanes. At the same time, operating expense increased $20 million, or 3 percent, over the comparable 1992 quarter. Container volumes handled also increased 3 percent.