Usually on the news, you see the 'troops' wearing "raid jackets"

http://www.sallyscopshop.com/products-page/raid-jackets/ 

unless they're going after a dangerous fugitive when they would be in tactical gear. I imagine the supervisory marshal would wear a suit and only perhaps show up at the press conference - behind the U.S. Attorney. I don't think the head guy/gal would wear anything other than a suit unless they were tagging along on a high profile raid to get some camera time. I could be wrong of course :-)

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken