I am a last year Ph.D student and intend to apply for a postdoc call starting in September. As I have not submitted my thesis yet, is it possible to apply earlier? And how can I ask my adviser to send recommendation letter while still I have not defended my thesis? ( I mean how can I explain my adviser this demand?)
Applying for a postdoc before defending your PhD is a very common situation which your adviser should be familiar with. Just say to your adviser that you are applying for a postdoc and that you would like him to write a letter of recommendation; there shouldn't be any more to it than that.