By Phil Wahba

NEW YORK (Reuters) - U.S. retailers are expected to report healthy sales gains for June, as bargains brought in nervous shoppers, leaving some wondering whether too much discounting may crimp second-quarter profits.

Consumers are still under a great deal of pressure from high food and gasoline prices and lingering economic uncertainty.

Some 25 top chains ranging from Target Corp <TGT.N> and Kohl's Corp <KSS.N> to J.C. Penney Co <JCP.N> and Ross Stores Inc <ROST.O> report June sales on Wednesday and Thursday.

Analysts on average are expecting them to post a 4.6 percent increase in June sales at stores open at least a year, according to Thomson Reuters, with discount chains leading the way. That compares with a gain of 3.1 percent in June 2010.

"June was a decent month with a lot of discounting. Consumers were expecting discounts; no one wants to pay full price," Craig Johnson, president of Customer Growth Partners, told Reuters.

Retailers such as Children's Place Retail Stores Inc <PLCE.O> and Gap Inc <GPS.N> used increasingly steep discounts to lure shoppers. Gap, for example, offered online shoppers 25 percent off in mid-June, and two days after that offer expired tried to entice them with a 35 percent discount.

Investors will be keeping an eye on how deep discounts may have affected margins and whether they will continue in July, the last month of retailers' fiscal quarter.

Johnson and many Wall Street analysts cautioned against reading too much into June results, given that that month is when retailers typically cut prices on spring and summer items to make room for back-to-school and fall merchandise.

Discounting is expected to continue into July, denting gross margins, Janney Capital Markets analyst Adrienne Tennant said in a note to clients.

"Promotions were high across the board," said Nomura Equity Research analyst Paul Lejuez.

In May, same-store sales rose 4.9 percent, below the 5.4 percent increase that Wall Street expected.

BIGGEST GAINS AT DISCOUNT CHAINS

U.S. consumers grew more pessimistic in June about the economic outlook. The Thomson Reuters/University of Michigan Survey of Consumers final June consumer sentiment index fell to 71.5 from 71.8 in the preliminary June reading, below economists' forecasts.

Discount chains, especially those that sell gasoline at lower prices, should clock in the biggest June sales gains, according to Wall Street estimates.

Costco Wholesale Corp <COST.O> is expected to report a 11.5 percent increase, or an 11 percent rise excluding gasoline sales, while BJ's Wholesale Club Inc <BJ.N>, which last week said it was selling itself to two buyout firms, should post a 7 percent gain.

Several analysts said that high gas prices and shopper anxiety were curbing trips to the mall to go shopping.

Still, middle-class and more affluent shoppers have hit stores with gusto, and high-end chains like Saks Inc <SKS.N> and Nordstrom Inc <JWN.N> are expected to post the biggest gains among department stores.

Wall Street is expecting Gap, which is trying to reignite its namesake brand, to report a companywide drop of 2 percent in same-store sales. That would make it one of only two chains tracked by Thomson Reuters to have declining same-store sales for June. The other is teen retailer Hot Topic. <HOTT.O>

Despite the uncertainty, Customer Growth's Johnson is expecting the best back-to-school season since 2006, helped by pent-up demand for clothing, provided gas prices cooperate.

"The fear factor comes in at $4," Johnson said, referring to gasoline prices. A gallon of gas on average costs $3.56, according to the American Automobile Association, far above the year-ago level of $2.72 but still lower than the prices in recent months.

(Reporting by Phil Wahba, additional reporting by Jessica Wohl in Chicago, editing by Matthew Lewis)