Army Won't Pay 15 Pct of Halliburton Bill  WASHINGTON (Reuters) - The U.S. Army will withhold payment  on 15 percent of future invoices of Halliburton Co.'s &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=HAL.N target=/stocks/quickinfo/fullquote"&gt;HAL.N&lt;/A&gt;  logistics deal in Iraq due to a billing dispute that could cost  the company \$60 million a month, the military said on Tuesday.