(Adds background, quote, details about revenue, margin, capital ratio)
Feb 8 (Reuters) - National Australia Bank Ltd NAB.AX , the country's No. 4 lender by market value, on Thursday reported a 3 percent rise in first-quarter unaudited cash profit after bad and doubtful debt charges declined.
NAB posted unaudited cash earnings of A$1.65 billion ($1.29 billion) for the three months ended Dec. 31, in line with a Morgan Stanley (NYSE:MS) estimate of about A$1.7 billion.
Australia's four major banks have logged record profits for years, but have been hit by a series of scandals, forcing the government to order a year-long inquiry into the sector. and doubtful debt charges fell 23 percent to A$160 million for the period, the bank said in a statement.
"We are on track to deliver the targets announced with the FY17 results, including an estimated $1.5 billion increase in investment by the end of FY20. Cost savings of more than $1 billion continue to be targeted by end FY20," NAB Chief Executive Officer Andrew Thorburn said in a statement.
The bank said first quarter operating expenses rose 4 percent in part due to higher investment spending, while revenue edged up 1 percent.
NAB's common equity tier-1 ratio rose to 10.2 percent at Dec. 31 from 10.06 percent on Sept. 30. The Australian Prudential (LON:PRU) Regulation Authority said last year that the "Big Four" banks were required to raise their Tier 1 capital ratios to 10.5 percent by 2020. interest margin declined during the period, but was broadly stable after excluding the impact from Markets and Treasury, the bank added.
($1 = 1.2788 Australian dollars)