Major retail chains reported yesterday that sales for the first half of 1981 soared above last year's levels, propelled in part by good Father's Day sales, good weather and the fact that last year's sales were so rotten.

Sears Roebuck and Co., the nation's largest retailer, reported a 17.8 percent increase in domestic merchandise sales -- the largest year-to-year increase for the June period since 1973. K mart Corp., the second largest retail chain, said that sales were up 17.1 percent over last year.

Wal-Mart, a chain of 354 stores with headquarters in Arkansas, reported one of the largest gains at 46 percent; Dayton-Hudson, which operates 851 stores, reported a 31.4 percent increase, and Zayre Corp.'s sales were up 20 percent.

Washington area stores reported the same trends, with sales surpassing expectations in some cases. But some retailers and analysts warned that what appears to be progress may just amount to catching up from losses last year.

"The economy is not as strong as sales indicate," said Jeffrey B. Edelman, a retail trade analyst for Dean Witter Reynolds Inc. "The level of sales we're seeing now is consistent with the slowing of the economy, but year-to-year sales are higher. Last year's sales were depressed by credit controls."

Credit controls were imposed by the Carter administration in March 1980 and lifted in July. "The consumer got quite scared" and drew back, Edelman said.

Yesterday the Conference Board reported that its consumer confidence index advanced in June for the fourth month in a row. Another measure used by the private research organization, the buying plans index, also climbed.

Several Washington area retailers said that in contrast to the leveling of sales that Edelman said he is seeing nationally, sales here are continuing to improve. Few were willing to predict, however, how long that might last.

"For the last few months sales have been relatively strong," said Martin Pfeifer, vice president for finance at W. Bell & Co., a Rockville-based catalogue and showroom retailer. "I think we're going against a rather slow period last year, but we also have had an increase in market acceptance," he said.

David Mullen, president of Woodward & Lothrop, said that the department store chain's business "is running much stronger than we had planned. We had an excellent month in June." Father's Day business was good, apparel sales have gone well and a rainy weekend brought shoppers into the stores in greater numbers than might have been anticipated over the Fourth of July holiday weekend.

But he added, "I think the current good business is really too sporadic to interpret as a directional turnaround in business. I think we're going to continue to play it by ear."

Other major chains reporting sales results included J.C. Penney Co., where sales rose 8 percent, and F.W. Woolworth Co., where sales increased 3.2 percent. The lower rate of increase at Woolworth reflected a decline in foreign sales related to a decline in the value of the dollar. Montgomery Ward, a Mobil Corp. unit, reported that sales rose 10.2 percent.

Federated Department Stores, Inc., a chain that includes Bloomingdale's, reported that sales were up 15.9 percent.