لجنة المنافسات والمشتريات - Competitive Procurement Committee;
لجنة المناقصات والمشتريات - Tenders and Purchasing Committee

"Competitive Procurement" is a general term for purchasing through a competitive process. An example of use:

The Competitive Procurement Committee met on April 28, 2008. The Proposer had been invited to the meeting. The committee reviewed the qualifications section of the proposal received and scored and ranked them. After the qualifications sections in each of the proposals had been reviewed and ranked, the cost proposal was opened, reviewed and ranked by the Competitive Procurement Committee.
http://www.swfrpc.org/content/Agendas/2008/May/Item3c.pdf

Tenders are a specialized method of procurement. In مناقصات the award of the tender is based on price.

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Note added at 3 hrs (2008-06-07 21:12:58 GMT)
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are the two committees both part of one client (company, public body or whatever)?

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Note added at 13 hrs (2008-06-08 07:45:46 GMT)
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Probably the simplest is to translate them with different names in English as if they were two separate committees and not be concerned about what their relationship is to one another if you don't have any more context that explains that.