The Standard & Poor’s 500 Index hit another record high Tuesday, and the market should continue to gain, though in a moderate fashion, says Tobias Levkovich, chief market strategist for Citigroup.

"Valuation remains attractive, while implied long-term earnings growth expectations have stayed subdued," he writes in a commentary obtained by CNBC.

"Buyback activity has stepped up, and money has begun to flow into equity funds. Even intra-stock correlation has rebounded, while sentiment is no longer complacent. Hence, the market should grind higher."

Editor's Note: I Wish I Were Wrong — Economist Laments Being Right. See Interview.

Stocks may encounter difficulties in the second half of the year, Levkovich notes. "But a summer slump driven by the old 'Sell in May' adage is not necessarily in the cards," he adds.

Levkovich maintains his 1,615 target for the S&P 500. It closed at 1,597.57 Tuesday. The S&P 500 could exceed the target, then dip below it and then rebound, Levkovich predicts.

Sam Stovall, chief equity strategist at S&P Capital IQ, has a positive outlook on stocks too.
"What we have seen is the market, which was going through a bit of self-doubt if you will, has started to feel a little more confident about its prospects," he tells CNBC.

Many experts credit the stock market’s strength to the Federal Reserve’s massive easing program. "The market is at a high here, and a lot of that seems to be driven by the faith in central bankers," Gary Flam, a portfolio manager at Bel Air Investment Advisors, tells Bloomberg.

Editor's Note: I Wish I Were Wrong — Economist Laments Being Right. See Interview.