The largest copper producer in the Philippines, Marcopper Mining Corp., may be forced to halt operations because of heavy losses and growing debt.

The company suffered a loss last year of more than 160 million pesos (US$8 million), though that was an improvement on the 341 million pesos of 1986.But its current liabilities exceed current assets by 335 million pesos and there was a capital deficiency of 345 million pesos last Dec. 31, according to its auditors.

Marcopper is 40 percent owned by Placer Development Co. of Canada and 60 percent by a government agency that sequestered the remainder as part of a campaign against corruption.

The auditors, Joaqin Cunanan & Co., an affiliate of Price Waterhouse, say Marcopper is in default on certain loan agreements and that some creditors have indicated they will take action.

Marcopper's management is pinning its hopes on developing what it says is a 200-million-ton reserve known as San Antonio, a project suspended earlier when copper prices fell. The company has invested more than 600 million pesos at the site.

It borrowed US$37 million in foreign currency loans from two consortia led by Chase Manhattan Bank and BA Asia Ltd., a unit of Bank of America, to finance the San Antonio project. Those loans are now reported to be in default, though no one was available Thursday at either bank to comment.

Marcopper acknowledges that San Antonio is crucial to its survival, and is seeking further tax breaks from the government and a restructuring of outstanding loans.

The outside auditors argue that the investment in San Antonio may never be recovered. They also say ore reserves on Marinduque are being rapidly exhausted.

All these factors indicate that the company may be unable to continue in existence, they warn.

Mining in the Philippines overall showed improved earnings last year, though output generally was lower.

The price of copper hovered around 81 U.S. cents a pound for most of the year, nearly 30 percent higher than the 62 cents of 1986. In December, it was around US$1 a pound.

Copper output in the first half of last year was down 2 percent to 106,212 metric tons against 108,336 tons in the corresponding 1986 period. Full-year figures aren't yet available.

The contribution of copper to the mining sector slipped to 28.5 percent in the period from 35.7 percent in 1986, according to the National Economic and Development Board.

Marcopper isn't the only sufferer.

Atlas Consolidated Mining & Development Corp. is having talks with the Australian-based entrepreneur Alan Bond in an attempt to get a cash injection of as much as $250 million.

Atlas has recorded a string of losses since 1984, aggregating $160 million through 1986. The company showed a net loss of $14,000 for the six months through last June 30, about half the deficit of the 1986 first half.