* Strike comes amid CESCO/CRU copper conference in Santiago
* Work stoppage to cost Codelco more than $35 mln
* Private mines operating normally but some have delayed shifts
By Anthony Esposito and Antonio De la Jara
SANTIAGO, April 9 (Reuters) - Workers at Chile's state mining company Codelco went on a 24-hour strike on Tuesday to demand better job security and safety improvements, but miners at some private copper companies just delayed the start of their shifts.
Codelco union bosses timed the strike to coincide with the international copper industry's CESCO/CRU conference in Chile's capital, the biggest meeting of its kind in the world.
While the 24-hour strike is not expected to have much impact on output from the world's No. 1 copper producing country, Codelco workers have steadily pressed management for better conditions over recent months, raising the specter that a steady drip-drip of labor actions could end up slowing output.
Tuesday's strike comes on the heels of an extended port strike, which delayed copper shipments and cost Chile's fruit and forestry producers untold millions.
Most ports in Chile, including key ports in the mineral-rich north, have returned to normal operations after the extended strike.
"I want to express my worry about what we've seen in recent days, for example the port strike which caused great damage to Chile's economy, to job creation and to our workers. And the copper strike which is happening now will also cause great damage," Chilean President Sebastian Pinera said.
Though Chile boasts enviable copper reserves and is expected to produce 5.58 million tonnes of copper this year, nearly a third of world supply, miners are reeling from steep costs, tumbling ore grades and an uncertain power supply. Intermittent labor scuffles have also kept miners on guard.
The stoppage will cost Codelco, the world No.1 copper producer, up to $35 million in lost operational revenues, the company said, adding it had adopted contingency plans to protect equipment and installations.
"The strike is under way and it has been a success," said Jaime Graz, union leader at Codelco's giant Chuquicamata mine. "This is a call to attention to the company's management because of the poor security conditions and urgent need for pension and healthcare improvements. It's not just about making more money."
Chile's November presidential elections are seen galvanizing labor as unions seek to make their issues heard.
Codelco will try to reach an agreement with workers to recoup lost production, Chief Executive Thomas Keller told reporters.
The state miner owns about 11 percent of the world's copper reserves and is expected to produce 1.7 million tonnes of copper this year, or just under 5,000 tonnes per day.
Workers at private mines, including BHP Billiton, Anglo American and Antofagasta Minerals, only adhered partly to the national strike, even though the union representing them initially said it would join the labor action.
Protesting workers delayed the start of the 8 a.m. (1100 GMT) shift by two hours at BHP Billiton's Escondida, the world's largest copper mine, and blocked the access road to Anglo American's Los Bronces mine.
"The workers adhered to the protest, but only for a limited amount of time, a couple of hours. This isn't an action against the company, it's a protest for the problems which at the national level haven't been resolved," said Marcelo Tapia, head of Escondida's union.
Top executives at Anglo American and Antofagasta said there could be some shift delays at their local mines, but operations were functioning normally.
Operations "are functioning ... there might be some delay in the start of the shifts, but operations are functioning," Antofagasta Chief Executive Diego Hernandez said.
Workers at the world's No. 3 copper mine, Collahuasi in the Andean nation's copper-rich north, decided not to strike and operations there are normal, a union leader said.
"We're not going to participate in this strike because it's an exploitation of workers' demands ... Collahuasi's operations are normal," Collahuasi union secretary Lincon Espinoza told Reuters.
Collahuasi is owned by Anglo American Plc, Xstrata Plc and a group of Japanese companies led by Mitsui & Co .