Lenders are offering larger discounts than ever for introductory ARM rates, but borrowers are getting smaller interest-payment savings from ARMs relative to fixed-rate loans, according to Freddie Mac’s annual survey of adjustable-rate mortgages. “The Federal Reserve ratcheted up short-term interest rates five times over the last half of 2004,” said Frank Nothaft, Freddie Mac’s chief economist. “Long-term mortgage rates were not affected much, but initial rates on ARMs rose by about 40 basis points…