Q: If one is just starting out a weight training program can one gain muscle mass even if there is a calorie deficit?And secondly, if I burn as many caloires as I consume will the muscle mass that I gain be equal in weight to the fat that Is lossed. theoretically I shouldnt gain or lose weight if calories in=calories out so a pound of muscle gained should be accompanied by a pound of fat lost.

A: Yes, beginners can typically lose fat and build muscle at the same time (in other words, gain muscle mass while in caloric deficit). For how long this continues depends on the person's genetics, training, diet, and body composition. Eventually everyone hits a sort of plateau of body composition and training level after which they can no longer build muscle and lose fat simultaneously at a reasonable pace. At that point they would be well advised to focus on one goal or the other. Many people are able to achieve above-average physiques before hitting the plateau, but it is extremely rare for somebody to lose enough fat to see the six-pack while simultaneously building muscle.

If you start out with an average or an above average physique, then the length of time before you hit this plateau will probably be pretty short, so once you notice that you've stopped making progress you should decide whether losing fat or building muscle is more important to you and structure your diet accordingly (your training will be essentially the same in either case). If you are unsure which to go with, think about how much extra fat bothers you. If it bothers you a lot, you should probably continue with fat loss because you won't like seeing the extra fat you put on while eating to build muscle. If you care about building muscle enough that a little extra fat doesn't bother you, then by all means go for a muscle-building diet! Once you've gained significant muscle mass then you can decide to cut the fat and the newly gained muscle will make that process that much easier.

What you said about gaining one pound of muscle for each pound of fat lost is also correct -- if you eat maintenance calories (in other words, just enough to maintain your current weight), you will slowly burn fat and build muscle while keeping the weight constant. But that process will only proceed at a reasonable pace until you hit the plateau I mentioned before. Once there, the process slows down to such crawl that you will not want to wait for the results and again you will need to choose which goal to focus on first.