Tenneco Inc. reported a third-quarter profit of $7 million on Thursday, compared with a $117 million loss posted for the same period last year. Tenneco's 1988 third-quarter earnings amounted to 2 cents per share. Revenue for the 1988 quarter was $3 billion, compared with $2.8 billion last year. Third-quarter results included an after-tax loss of $42 million from discontinued operations of Tenneco Oil Co., which is being sold to several different buyers for an estimated $7.3 billion. That compares with a loss from discontinued operations of $101 million for the same period last year, which includes the discontinued operations for 1987 of Tenneco Oil and the since-sold Tenneco West operations. ``We continue to work toward further strengthening of our remaining businesses and managing them for maximum earnings, cash generation and return on assets through a focus on cost containment, efficiency enhancement and accelerated disposition of underperforming assets within each of the divisions,'' said James L. Ketelsen, chairman and chief executive officer. For the nine months, net earnings totaled $224 million, or $1.39 per share, compared with a net loss of $42 million for the 1987 nine-month period. Revenue for the nine months was $9.6 billion this year and $8.7 billion last year. With the sale of its oil and gas properties, Tenneco's biggest units will be the profitable natural gas pipeline and its Case IH farm equipment manufacturing sector. Tenneco also maintains shipbuilding, automotive packaging and chemicals units.