I don't think this is just an enterprising reporter. This was leaked, although probably not from the FBI.
First of all, this isn't an isolated report bringing up Iraq. There was the New Yorker article and the reverberations from that. At the same time, John Doe #2 and the Iraqi connection to the Oklahoma City bombing are suddenly brought up again and considered credible by the media. And there's this new anthrax-9/11 connection, with the implicit link to Iraq. This is all against the backdrop of Vice-President Cheney drumming up support for an attack on Iraq, virtually in public.
Secondly, it's hard to see how reporter's legwork would yield this story. Consider: a memo was written at the Johns Hopkins bioterrorism group which was circulated among top government officials. And then the newspaper report came out.
The most likely explanation is that one of these "top government officials" decided that it was time to get this out there, that the public had to be prepared for war with Iraq, and that they had to start deflating the Rosenberg thing. [It's almost true that anything that's widely circulated among top government officials gets leaked. The reports may not be believed -- witness some of the leaks about Vince Foster -- but they'll be leaked. After all, if lots of people know something, anyone can leak with impunity, since the source can't be easily determined.]
Alternatively, maybe the government officials did nothing, and the people at Johns Hopkins were dismayed that the memo had apparently not been taken seriously. So possibly someone at Johns Hopkins leaked it, just to bring it out and force the government to pay attention to it.
In any case, waiting for the threat to become "manageable" is wishful thinking. (This seems to have been Clinton's policy.) The fact is that the longer we wait, the more unmanageable the threat becomes. I'm sure the decision has been made that we just have to take whatever Saddam Hussein throws at us, because if we wait 10 years, it will be much worse. If we do it now, we will win. although it may be painful. In 10 years, it will be much more painful, and we may not even be able to win by that time. In other words, it's a war that will have to be fought sooner or later, and it's greatly to our advantage to do it sooner.