* Copper on track for second straight monthly drop
* COMEX copper breaks down below key trendline support
* U.S. regional manufacturing data adds to econ woes
* China bonded warehouse stocks on the rise in April (Recasts, removes Singapore dateline, updates New York copper price, adds quotes and details)
By Chris Kelly
NEW YORK, April 29 (Reuters) - Copper fell to its lowest level since mid-March on Friday, hit by chart-based selling and soft U.S. economic data that continued to offer proof of slowing growth in the world's largest economy.
In New York, the most-active July COMEX copper contract crumbled 10.35 cents to a session low of $4.1580 per lb, its lowest level since March 15. It was last at $4.1865, down 7.50 cents from Thursday's close.
Bearish technical momentum gathered pace after the front-month May broke down below key trendline support at $4.20, traders said.
(Graphic: http://link.reuters.com/tuk39r )
"In terms of the overall chart picture, we have taken out some support, and a lot of really good support that was around $4.21 (per lb)," said Scott Meyers, senior trading analyst with Pioneer Futures in New York.
"Right around the $4.15 level is where it should start to slow up and find some support. If we settle below $4.15 today I would think we can probably make a straight line towards that $4.0760 level."
Liquidation pressures mounted at the open after U.S. data showed factory activity in the country's Midwest slowed this month, potentially indicating some cooling in manufacturing.
"The Chicago PMI was another one in a string of numbers that have been disappointing," said Sterling Smith, an analyst for Country Hedging Inc in St. Paul, Minnesota.
"It's showing that growth is slowing greatly, if not coming to a complete stop," he explained.
Separate data showed U.S. consumer spending edged up 0.2 percent in March as households stretched to cover the higher cost of food and gasoline and inflation posted its biggest year-on-year rise in 10 months.
The reports come on the heels of disappointing U.S. growth figures and weekly jobless claims benefits on Thursday which cast a long shadow over growth expectations heading into the second quarter.
Copper was on track for a second-straight monthly loss, under pressure from mounting concerns about further interest rate tightening in Asia, Europe and Latin America.
Euro zone inflation edged up to 2.8 percent in April, well above the 2 percent target ceiling of the European Central Bank, which raised rates for the first time in two years earlier this month.
Copper inventories in warehouses monitored by the Shanghai Futures Exchange fell for the sixth week to their lowest level since mid-February.
Despite the steady fall of stocks in surveyed warehouses, Standard Chartered bank on Friday warned that China's copper inventories in bonded warehouses were still on the rise in April.
Stocks in Shanghai's bonded warehouses were hovering at around 650,000 tonnes, equivalent to roughly four weeks of China's domestic use and higher than the 200,000-tonne average over the past three years.
"What is worrying for bulls is that the majority of these copper stocks are tied to finance deals, meaning either that they were bought for the purpose of collecting bank loans, or they were unable to find immediate buyers," the bank said in a report led by analyst Judy Zhu.
"Either would indicate that there is no real demand backing these stocks; hence, we believe a surplus of the metal in China is imminent."
The London Metal Exchange (LME) copper three-month delivery contract closed flat on Thursday, its last trading day of the month, at $9,320 per tonne.
The most active Shanghai copper contract July, dropped 1.2 percent to 69,200 yuan.
The LME is closed on Friday for Britain's royal wedding, and will remain closed on Monday for a public holiday. Shanghai will also be shut. (Additional reporting by Carrie Ho in Singapore; editing by Rene Pastor)