(see related story on stock market, spread) Rome, April 29 - The average interest rate that Italy's 10-year bond fetched at a Treasury action was under 4% for the first time since October 2010 on Monday. The auction was a hotly awaited test of investor sentiment after Premier Enrico Letta's left-right government was sworn in on Sunday to end the deadlock Italy had endured since February's inconclusive general election. The Treasury sold six billion euros' worth of the 10-year and 5-year bonds it put up for action Monday. The average rate on the 10-year BTP dropped to 3.94, compared to 4.66% at an auction in March. The average rate on the 5-year bond was 2.84%, compared to 4.66% at the last equivalent sale.