U.S. Expresses Concern About UAL Pensions  WASHINGTON (Reuters) - The Bush administration expressed  fresh concern on Wednesday about the possibility bankrupt  United Airlines &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=UALAQ.OB target=/stocks/quickinfo/fullquote"&gt;UALAQ.OB&lt;/A&gt; might scrap its employee pension  plans, which would shift the burden of paying benefits to the  government.