Credit Suisse has revised down its U.S. GDP forecasts for the first half of 2011. The firm now expects 2.5% real GDP growth in Q1, down from its previous forecast of 3.5%. Its Q2 forecast was also revised down to 3.3% from 3.7%. However, the firm's 2011 second half forecasts remain unaltered at 3.8% and 4.0% for Q3 and Q4, respectively. Credit Suisse expects full year 2011 growth of 3.4% on a year-over-year basis and 3% on an annual average basis. This is down from its previous estimate of 3.8% and 3.3%, respectively. The firm sees 4.0% real GDP growth in 2012.Credit Suisse issued a statement saying: The first quarter's forecast revision is mostly due to current quarter accounting. The monthly building blocks that add up to GDP have consistently printed below expectations this quarter, defying the much rosier readings from other parallel evidence on the economy (such as the ISM surveys). The list of GDP "source data" disappointments includes home sales, housing starts, capital goods shipments, non-residential construction, federal spending, and a sharp increase in the trade deficit. Most importantly, the GDP's largest building block - consumer spending - is slowing sharply on a sequential basis, on track for less than 2% growth in Q1, compared to 4% growth in Q4. Our revision to second quarter growth is partly a consequence of higher oil prices and the negative effect on real income growth. Consumer confidence gauges also fell sharply in March, presumably due to higher gasoline prices. Another reason for our Q2 downgrade is housing, particularly the 22% plunge in February housing starts. Falling starts will impact future readings on construction outlays and the associated GDP component - residential investment.