SENATE APPROVES TWO CURBS ON SST
Sen approves bill sponsored by Sen Magnuson requiring that liner be quieter in every stage of operation than present jetliners; measure and last-minute efforts to answer craft's environmental critics seen indicating waning support for development on eve of Sen vote; measure seeks rewriting of contracts with Boeing Co and Gen Elec to stipulate that engines must be quieter than those on subsonic craft on take-off and landing, with maximum of 108 decibels of sideline noise; uncertainty over reduction of engine noise without loss of craft's thrust or range discussed; Sen approves ban on flights over land areas; Sen Proxmire says this will exclude liner from payoff routes across US and limit mkt for craft below level necessary for Govt to recoup investment; US lines seen holding off on purchase of foreign supersonic liners as long as US craft is being developed but Amer Airlines pres Spater warns cancellation of project will force carriers to purchase foreign liners to protect their competitive position; Pres Council of Econ Advisors member Dr Houthakker, in reply to project dir Magruder statement that council concurred in his rebuttal of 15 economists opposing project, says rebuttal was developed by Magruder and not by council; says council has always supported development

