Representatives of Unocal Corp. and an investor group headed by Mesa Petroleum Co. Chairman T. Boone Pickens Jr. met over the past two days to settle the Pickens group's long-running battle to obtain control of the big oil company, but the talks broke off with no agreement, spokesmen for both sides said yesterday.

Mesa said Unocal initiated the talks. Unocal Chairman and President Fred L. Hartley had said on Monday, following his company's annual meeting, that he would be willing to buy out Pickens' 13.6 percent stake in Unocal at current market prices. Unocal has said it will not pay more than market price, or greenmail, and Pickens has said he won't accept greenmail -- although he would likely make a hefty profit on a buyout at the market price.

At Unocal's annual meeting Monday, Pickens apparently lost a key stockholder vote that would have expedited his $3.6 billion attempt to buy control of the company. Pickens has asked a federal court to overturn the stockholder balloting because of alleged irregularities, but if he is not successful, elements of Unocal's bylaws may prevent Pickens from resuming his attack on the company for a year.