Whereas the representation of the company is already mentioned before indicating the capacity of the representative, it leaves us with no option but to translate his title:

"This Agreement is made by: 1- ________ Company represented herein by Eng. _____________, its General Manager"

The literal meaning of the requested term: "person entrusted with general powers to run/manage the company or the authorized signatory"; hence the General Manager

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Note added at 4 hrs (2010-10-16 20:34:01 GMT)
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كلمة الإدارة هنا لا تشير إلى المدراء الذين يتولوا تدبير أمور الشركة وتسيير شؤونها، بل تعني "فعل" الإدارة نفسه، والدليل هو حرف العطف "بـ" وليس "من"