Reynolds Metals Co., the second largest U.S. producer, reported a bit of profit for 1982, but said it lost money in the last quarter.

The company, which is based in Richmond, made a profit of $7.7 million (26 cents a share) in 1982, compared to a profit of $86.7 million ($4.40) the year before.

Reynolds, however, did not make its money on its aluminum operations. Its 1982 profits came from an accounting change and from a stock market deal.

The company lost $19.8 million in the last three months of 1982, compared with a loss of $21.1 million in the fourth quarter of 1981.

Sales for 1982 fell to $3 billion from $3.5 billion, and fourth-quarter sales dropped to $669.7 million from $$787.1 million.

Reynolds said it expected to see an improved performance for the second half of l983.

Potomac Electric Power Co. officials reported yesterday the utility posted increased profits, higher kilowatt-hour sales and more electricity produced from coal during 1982.

Pepco earnings grew 6 1/2 percent to $119 million ($2.28) during 1982, from $109.7 million ($2.14) in 1981.

For the final quarter, Pepco posted profits of $25.1 million (46 cents), a 7 percent gain over 1981's $23.2 million (43 cents) earnings.

Operating revenues increased to $1.1 billion in 1982 from $1 billion, and to $244.8 million from $225.3 million in the fourth quarter.