Unocal Corp. said yesterday it would abide by a Delaware court ruling and accept shares held by an investor group led by Mesa Petroleum Co. Chairman T. Boone Pickens Jr. under Unocal's $72-a-share offer for 29 percent of its stock. The Pickens group owns 13.6 percent of the Los Angeles-based oil company.

But Unocal said it would appeal the court decision, and reserved the right to choose to drop the offer if its appeal is unsuccessful.

"Unocal intends to pursue all available legal procedures to obtain a change or reversal of the Delaware court's ruling," Unocal said in a letter to shareholders. "If Unocal is successful, it will not accept any Mesa shares for exchange. However, if the ruling remains unchanged and in effect at the time shares are to be accepted under Unocal's offer, Mesa's shares will be accepted."

The letter to shareholders accompanied new proxy materials sent to shareholders to inform them of Unocal's rescheduled annual meeting. A federal judge in Los Angeles last week postponed the annual meeting to May 13 from last Monday to give Unocal an opportunity to correct inaccuracies found by the judge in its proxy material.

Pickens' group continues to lobby for a further two-month postponement of the shareholders meeting.