The investment world's institutional bears -- who believe the U.S. economy is far from robust GDP growth, and at best will emerge from its worst recession in decades with only modest, gradual growth, an L-shaped recovery -- will try to seize on every Q2 earnings underperformance as yet another sign of overly-optimistic recovery expectations.

Conversely, the institutional bulls -- who see an economic recovery in Q3/Q4 -- will argue that lower, year-over-year earnings declines or in some cases actual earnings increases indicate that the recession is bottoming, perhaps even that the recovery has already started.

Hence, the impact of S&P 500 Q2 earnings reports on the stock market will likely hinge on not only actual earnings performance, but what those earnings suggest will happen in the U.S. economy in the second half of the year. Currently, the consensus among Wall Street analysts is that investors have bid up share prices too high, given the economy's overall weakness and doubts regarding the recovery's strength. Hence, a series of EPS underperformances by bellwether companies in Q2 will likely drive the stock market down in Q3.

Companies to keep an eye on

With that in mind, here are a few bellwether companies that will give investors a sense of how the economy is performing, where it's headed, and by extension, the earnings support for future stock market gains:

Alcoa (AA). Keeping with Wall Street tradition, Alcoa kicks off Q2 earnings season Wednesday, with analysts surveyed by First Call expecting the company to post a 34-cent EPS loss in Q2. Recent chatter suggests AA may exceed that Q2 loss by 1-2 cents.

FedEx (FDX). Investors should also keep an eye on FedEx Q2 performance, and earnings guidance for the year, given the relationship between increases in deliveries and economic growth. The First Call Q2 EPS estimate for FDX is 41 cents.

UPS (UPS). Likewise with delivery company UPS. The First Call Q2 EPS estimate for FDX is 49 cents.

General Electric (GE). Wall Street will also scrutinize performance of diversified industrial giant GE – the 'mutual fund in one company.' Investors should also pay close attention to GE's comments regarding international industrial business and demand. Any sign by GE that emerging market revenue is not showing signs of stabilizing will be interpreted bearishly by the market, as the next bull market will require sustained increasing in both international and U.S. demand. The First Call Q2 EPS estimate for GE is 23 cents.

Intel (INTC). Wall Street will also analyze Intel's results and comments regarding microprocessor demand. Any data or comments by Intel indicating that global chip demand is not rebounding would obviously be bearish for stocks. The First Call Q2 EPS estimate for INTC is 8 cents.

Google (GOOG). Capital is continually searching for growth and high return, and given Google's status as a premier growth company, Wall Street will also scrutinize the results from the world's most popular search engine. In general, expectations are low for GOOG, with the Street forecasting that the company will record its lowest quarterly, year-over-year earnings growth in its history in Q2. Hence, an upside EPS surprise by GOOG, and positive comments about Q3/Q4 will likely be bullish for U.S. stocks. The First Call Q2 EPS estimate for GOOG is $5.05.

Disclosure: Lazzaro has no positions in stocks, but does own shares in two Pimco Bond Funds: PHDAX and PYMAX.