Mobil Corp. announced yesterday that its earnings rose 49 percent in the final quarter of 1985, but its yearly income was off by 18 percent because of restructuring costs for its Montgomery Ward retailing subsidiary.

Two other oil firms, Atlantic Richfield Co. and Unocal Corp., reported lower earnings. Conrail, the government-owned freight rail carrier, Merrill Lynch & Co., and Procter & Gamble Co. all reported higher profits.

Mobil, the nation's second-largest oil company, said its fourth-quarter after-tax profit totaled $425 million ($1.04 a share) against net earnings of $284 million (69 cents) in the 1984 period. Revenue edged up to $16.3 billion from $16.1 billion.

For the full year, Mobil had a profit of $1.04 billion ($3.79), compared with earnings of $1.27 billion ($3.11) in 1984. Revenue slipped to $60.38 billion from $60.47 billion. Mobil said its 12-month profit was reduced by a one-time charge of $508 million for the restructuring of Montgomery Ward.

*Atlantic Richfield Co., the nation's No. 6 oil company, yesterday reported a 1985 loss of $202 million, compared with with net income of $567 million ($2.21 a share) in 1984. Fourth-quarter earnings amounted to $142 million (73 cents), compared with $285 million ($1.15) for the same period in 1984.

Lodwrick M. Cook, Arco's chairman and chief executive officer, blamed the loss on higher interest rates, lower domestic volumes and prices for crude oil and provisions for "unusual items."

Those items included $987 million taken in the second quarter to cover anticipated losses on the sale of an East Coast refining and marketing facility and a $514 million writedown for discontinued noncoal minerals operations.

*Unocal Corp., the No. 11 oil company, blamed its $134.7 million fourth-quarter loss on a partial writedown of its shale oil project, higher interest costs, antitakeover expenses and the loss of foreign tax credits. For the 1984 fourth quarter, Unocal, based in Los Angeles, posted net earnings of $153.4 million (88 cents a share). Revenue fell to $2.92 billion from $2.97 billion.

For the full year, Unocal earned $325.1 million ($2.36), down 53.5 percent from $700.4 million ($4.00) in 1984. Revenue rose, however, to $11.64 billion from $11.54 billion.

*Conrail said it had net income of $112 million ($4.06 per share) on revenue of $783 million for the fourth quarter of 1985, up from profits of $89 million ($3.30) on revenue of $792 million for the 1984 fourth quarter. The railroad said audited net income fell to $442 million ($16.02) on revenue of $3.2 billion in 1985, from $500 million ($18.50) on revenue of $3.38 billion in 1984.

The railroad attributed the rise in fourth-quarter 1985 net income in part to a 3.3 percent improvement in carloadings and Conrail's efficiency improvement programs.

Conrail's cash balance at year-end 1985 was $910 million compared with $846 million at the end of 1984.

Conrail officials cited the 1985 profits as evidence the railroad could stand alone as an independent railroad in the future. The Reagan administration has proposed selling Conrail to Norfolk Southern Corp. for $1.2 billion, a merger under review by Congress.

*Procter & Gamble Co. said earnings rose 15 percent and sales 20 percent for its second quarter ended Dec. 31. Earnings for the quarter were $165 million on sales of $3.87 billion, up from $137 million and $3.38 billion, respectively, in the 1984 period. Earnings per share improved to 99 cents from 81 cents.

The increases reflect in part results of Richardson-Vicks Inc., which P&G acquired in October for $1.2 billion. For six months ended Dec. 31, earnings were up 15 percent at $415 million ($2.48 a share) on sales of $7.47 billion, compared with earnings of $360 million ($2.15) on sales of $6.86 billion for the first six months of 1984.

Procter & Gamble, based in Cincinnati, makes and sells laundry and cleaning products, personal-care products, pharmaceuticals and food and beverage products.

*Merrill Lynch & Co. said yesterday that the rallies in the stock and bond markets helped its fourth-quarter profit more than double from a year earlier as revenue climbed 24 percent.

Merrill Lynch, parent of the nation's largest brokerage house, said net income jumped to $62.7 million (62 cents a share) in the fourth quarter from $29.6 million (31 cents) a year earlier. Revenue rose to $2.02 billion from $1.64 billion.

Merrill Lynch's profit for all of 1985 also more than doubled, to $224.3 million ($2.26) from $95.3 million ($1.03) in 1984. Annual revenue was up 18 percent to $7.12 billion from $6.04 billion.