The Obama administration is mulling a raft of emergency fixes to stimulate the economy before the midterms, including an extension of the research and development tax credit and new infrastructure spending, according to several people familiar with the situation. Administration officials have been huddling almost continuously during the past week, brainstorming for ideas that would boost employment without hiking the massive federal deficit — with Treasury Secretary Tim Geithner rushing to the West Wing for further consultations late Thursday. The White House press office on Thursday refused to say how much a financial package might be, other than to say it won’t be a “second stimulus.” But the administration will have a tough time selling nearly any package to some Democrats who increasingly blame the president and his ambitious legislative agenda for their own dismal prospects this November.