The nation's major retailers yesterday reported generally moderate sales gains for April.

One reason cited for the results was that Easter Sunday fell this year on April 10 last year it fell on April 18, giving shoppers more time in the month to make pre-holidy purchases.

Sears, Roebuck & Co. said sales in the month totaled $1.3 billion, a 12 per cent gain over April 1976 sales of $1.2 billion.

Montgomery Ward reported an 11.3 per cent gain in sales for month, to $344.1 million from $309.1 million. Sales for the first 13 weeks of the year were up 12.2 per cent to $1.01 billion from $900.9 million for the same period a year ago.

F.W. Woolworth Co. called its 3 per cent sales gain in the month a "a minor" one. Sales rose to 408.7 million from $307.4 million.

"Foreign sales, notably those in Canada, were unsatisfactory because of lower comparative exchange rates and economic uncertainties," Woolworth said.

J.C. Penney Co. Inc: said its 4 per cent increase was due primarily to strong sales of sportswear, sporting goods and automotive items. But generally, apparel spending was "subdued," Penney said.

For the month, sales rose to $615 million from $586 million.

S.S. Kresge Co. said its sales gained 18.7 per cent in the quarter, to $739.7 million from $623.3 million.

Among other large retailers:

Dayton Hudson Corp. reported sales were up 7.6 per cent in April, to $1322 million from $123 million.

Carter Hawley Hale Stores Inc., which operates department, book and specialty stores including Nieman-Marcus and Bergdorf Goodman, said sales rose 2.5 per cent, to $97.1 million from $94.8 million.

Zayre Corp.'s sales rose 15 per cent, to $383 million from $87 million.

Caldor Inc. recorded a 30.8 per cent sale gain, to $26.7 million from $20.4 million.

Vornado Inc. sales declined 2.5 per cent, to $76.7 million from $78.8 million.