Poor Boy in Corporate

I am a Engineering Graduate, now i am working in R&D organization. My problem is i can speak very comfortable with one to one but unable to do the same in group. like in Group Discussions I can't express my views exactly , some times even though i know something not able to express. More over i worried about my carrier if it carry's like this. when ever i stand in front of public i ll get tense , heartbeat runs very fast , my tone gets reduced{several are there} ... Plz help me idon't want end up my life with this fear