What do u mean by "more secure"? In a 64-bit system? It shouldn't be. Both in terms of secure storage or secure channels via the internet.
In anycase, I am going to presume that u are talking about the key sizes for encryption - b/c that wud only make sense for ur question.
In which case 64-bit keys are considered to be "insufficient". It can be broken with brute force given sufficient computing power. You or I wouldn't be able to on our pewny FX-55 or FX-57's even. But the government could easily. 80 bit is "more" acceptable but it's considered to be insecure as well. The standard these days is 128-bit. The government uses 192-bit for "Secret" information. And 256-bit keys for "top secret" information. Read up on the AES specification (which is the Rijndael system these days) and you can learn more about this topic.
For asymmetric key encrption (RSA, Diffie Hellman, etc.) I believe 512 is the bare minimum. 1024-bit is recommended. Don't quote me on this though. b/c I can't remember exactly. And it depends on the system too. If you wanna know more about encryption keys and such, post away!
I'll try to answer them.