Thanks, Jim.  I studied this video piece closely.  But it did not address the issue of mixed footage, which is the underlying reason for the varying Program Monitor screen sizes of images.  Essentially, if I choose a Sequence setting to accomodate my 1280 x 720 (1.0) footage, then my 1440 x 1080 (1.3333) footage is enlarged in my Program Monitor.  By contrast, if I choose a Sequence setting to accomodate my 1440 x 1080 (1.3333) footage, my 1280 x 720 (1.0) footage is reduced in my Program Monitor.

I should point out that I was indeed able to create a sequence for each footage type file.  And both Source and Monitor image sizes matched.  But as soon as I created a new sequence and dropped clips from the two different footages into it, I was right back where I started.

I attempted using Interpret Footage to try and match footage.  But the available selections there do not accomplish this.

So I suppose the question is:  How does one conform mixed footage like those listed above so that they match in the Program Monitor and consequently, when exported?

Thanks 

Thanks, Harm.  I understand what you're saying.  And I fully intend to choose a 720 sequence as that is the lowest resolution of my mixed footage.  But I'm still trying to figure out how to modify the 1080 footage in my 720 sequences so that the Program Monitor image size is normalized to match the already properly sized 720 footage.  What methods do I employ to adjust the 1080 footage, or, for that matter, any other mixed footage which does not match the 720 sequence settings in order to get the program monitor to properly size-match all the footage?  Thanks.

Thanks, Jim!  I had looked for such a shortcut while working with the files in the Project Panel, but didn't see anything like that.  Never thought to check the Timeline clips.  Most grateful.