It's very easy to perform with SubGit.
$ svnadmin create svn.repo
$ subgit configure svn.repo
$ nano svn.repo/conf/subgit.conf to specify a path to your bare repository (you may use "git clone --bare <URL>" if you have none locally)
$ subgit install svn.repo
After conversion your SVN and linked Git repository will be in sync: every Git push will be translated to SVN commit and vice versa. To break translation run
$ subgit uninstall svn.repo
While translation SubGit will try to preserve commit dates, tags, ignores, merges, EOLs, branches and so on, as it is possible. I can't say the same about git-svn repository.