Tenneco Inc.'s profits fell 46.1 percent in the fourth quarter of 1984, reflecting what the diversified energy company yesterday called depressed conditions in petroleum refining, petrochemicals and the agricultural and construction equipment industries.

Meanwhile, Lockheed Corp. has reported record earnings and sales for the year.

Houston-based Tenneco is a leading energy and natural gas pipeline company. It also has interests in shipbuilding, insurance, paper products and automotive equipment. It owns JI Case Co., a manufacturer of agricultural and construction equipment, which acquired International Harvester Co.'s troubled farm equipment business last month.

Tenneco's fourth-quarter earnings fell to $130 million (80 cents a share) from $241 million ($1.63) in the same period a year earlier. Revenue was $3.8 billion, virtually unchanged from 1983.

Earnings were reduced by a $95 million pretax write-down for current and planned closings of certain petrochemical operations, "which were necessitated by depressed market conditions," Tenneco said.

For all of 1984, profits slipped 11.9 percent to $631 million ($4.01) from $716 million ($4.75) in 1983. Revenue rose 3.5 percent to $14.9 billion from $14.4 billion.

Higher sales volumes of natural gas and crude oil products helped boost operating income for the company's oil exploration and production division, Tenneco said. Pipeline operations also experienced improved operating income for the year, primarily because of increased sales of natural gas.

* Lockheed Corp. said its fiscal 1984 earnings were $344 million ($5.28 a share), a 31 percent increase over fiscal 1983, officials said.

Fourth-quarter net earnings were $109 million ($1.65), compared with $84 million ($1.30) for the same period in 1983.

Sales for 1984 totaled $8.1 billion, an increase of $1.6 billion over 1983 sales of $6.5 billion.

Lockheed Chairman Roy Anderson attributed the increase to revenue from such programs as the Trident II missile system and the Space Shuttle.