J. C. Penney Co., the nation's third-largest retailer, said yesterday that its fourth-quarter profits increased 3.8 percent over a year ago, but declined 8.6 percent for the year.

At the same time, the No. 10 retailer, R. H. Macy & Co., said profits for its latest quarter gained 5.1 percent, and Firestone Tire and Rubber Co. reported higher earnings for its first quarter.

Penney, which is based in New York, said its net income for the three months that ended Jan. 25 came to $224 million ($3 a share) compared with $216 million ($2.89) in the same period of 1984. Sales rose 5.8 percent to $4.69 billion from $4.43 billion.

The company's retail divisions had a 24 percent increase in net income for the three months, before the impact of the last-in-first-out method of inventory valuation, said Chairman William Howell.

For the year, net income fell to $397 million ($5.31) from $435 million ($5.81) in 1984. Twelve-month sales rose 2.2 percent to $13.75 billion from $13.45 billion.

*R. H. Macy, which is based in New York, said net income for its fiscal second quarter, which ended Feb. 1, came to $106.3 million ($2.06 a share) compared with $101.1 million ($1.98) a year earlier.

The latest quarter was a 13-week period compared with 14 weeks in the period a year earlier. Sales rose 3.4 percent to $1.505 billion from $1.455 billion. However, the increase came to 6.5 percent, excluding 1984's extra week.

*Firestone Tire & Rubber Co. reported profits improved in its first quarter, despite a drop in revenue. Income totaled $82 million ($2.03 a share), up from $17 million (38 cents) for the same period in 1984.

Sales for the quarter that ended Jan. 31 totaled $861 million compared with $903 million in 1985. Company officials said 1986 results were helped by the adoption of new pension accounting standards recently issued by the Financial Accounting Standards Board.

A gain of $66 million ($1.63) resulted from the required recognition of income that was deferred on the termination of Firestone's salary pension plan in 1984.