1. Export as a Quicktime Movie with Current Settings and check the 'Make Movie self-contained'. I don't know if keeping it unchecked would make a difference.
2. Now open this full resolution file in Compressor and choose the following export options.
3. In the Settings window, under format, choose 'Quicktime, H.264' and drag it onto the file above.
4. Once you set the destination, click on the file. Now on the Inspector window, you will see the options available.
5. Now click on the second(Encode) button and click on Video Settings. Change the dimensions to 1280*720. Keep the setting as H.264 and in the bitrate change it to the desired value. For a 40 min HD video, we set the bitrate at 4000 kbps to keep it under 2 GB. Use the bitrate that would work best for you.
One question may arise as to why we need to export/convert to a Full resolution video before compressing on compressor. 1. To free up FCP when you are using compressor. 2. To speed up the compression process as opposed to exporting from an FCP sequence. (pic courtesy from ken's fcp)