HALIFAX, Nova Scotia (Reuters) - Defence chiefs from the United States and Canada said on Friday that budgetary pressures would not derail development of the F-35 Joint Strike Fighter, saying there was no real alternative to what has become the Pentagon's costliest weapons program. US Defence Secretary Leon Panetta said flatly he was confident Congress would approve funding for the F-35, which is facing fresh scrutiny for possible cuts as lawmakers weigh how to scale back the US deficit. Two days ago Canadian Defence Minister Peter MacKay expressed concern about reports of delays in F-35 delivery and said his government was in direct talks with manufacturer Lockheed Martin Corp.