ANT do have sshexec and scp task that may read encrypted ssh private key by passing password to the task. This isn't secure at all.
The Pageant from Putty stores private key that may used for SSH authentication anytime. Is there a way to make ANT and Pageant work together for SSH public key authentication?
ANT uses jsch as it's ssh implementation. This project has recently created a ssh agent proxy, but I don't believe it's integrated into the ANT task yet.