Sears, Roebuck & Co., the nation's No. 1 retailer, said Tuesday it is selling less merchandise but making more money.

Sears said its third quarter sales were $4.46 billion, down 1.9 percent from the same period last year when sales were $4.54 billion.

But earnings rose 4.5 percent to a record $233.5 million, or 73 cents a share, from $225.3 million, or 71 cents a share.

"Our basis sales program is showing good sales increases," said Edward R. Telling, Sears chairman and chief operating officer. "And the lost sales are all in promotional items, as we intended."

"We expect the same thing to happen in the fourth quarter," said Sears spokesman Ernest L. Arms. "We're cutting back the discounts we're offering, so we're making more profit on the items we sell."

Earnings for the nine months ending Oct. 31 was $591.6 million ($1.84 per share), 0.9 percent above the record $586.2 million, ($1.84) in the first nine months of 1977.

G.C. Murphy Co., retailers, also reported third quarter earnings gain, posting 82 cents a share, compared to 62 cents a share in the similar period last year.

Murphy reported profits of $3.232 million on sales of $167.7 million in the third quarter. Last year, the company made $2.430 million on sales of $157.4 million.