According to the article, the FBI knows which Bush officials leaked Plame to Novak. Here's a direct link to the article, and a snip:
http://www.prospect.org/print-friendly/webfeatures/2004/02/waas-m-02-12.htmlTwo government officials have told the FBI that conservative columnist Robert Novak was asked specifically not to publish the name of undercover CIA operative Valerie Plame in his now-famous July 14 newspaper column. The two officials told investigators they warned Novak that by naming Plame he might potentially jeopardize her ability to engage in covert work, stymie ongoing intelligence operations, and jeopardize sensitive overseas sources.
These new accounts, provided by a current and former administration official close to the situation, directly contradict public statements made by Novak. He has downplayed his own knowledge about the potential harm to Plame and ongoing intelligence operations by making that disclosure. He has also claimed in various public statements that intelligence officials falsely led him to believe that Plame was only an analyst, and the only potential consequences of her exposure as a CIA officer would be that she might be inconvenienced in her foreign travels.
The two administration officials questioned by the FBI characterized Novak's statements as untrue and misleading, according to a government official and an attorney official familiar with the FBI interviews.
One of the sources also asserted that the credibility of the administration officials who spoke to the FBI is enhanced by the fact that the officials made their statement to the federal law enforcement authorities. If the officials were found to be lying to the FBI, they could be potentially prosecuted for making false statements to federal investigators the sources pointed out.