Texas International Co. rejected yesterday a takeover offer from UNC Resources of Falls Church, but UNC said it is not giving up its bid to buy Texas International.

Meeting in Oklahoma City, Texas International's board of directors unanimously turned down UNC's offer of $22 shares and issued an announcement calling the bid "grossly inadequate."

From Falls Church, UNC promptly replied that it was "disappointed by UNC's action and put out a statement saying its "interest in acquiring Texas International continues." UNC said it is "evaluating its available alternatives," one of which is to make a higher bid for Texas International.

Texas International said its rejection was based in part on advice from its investment bankers, E. F. Hutton Co.

The Oklahoma oil and gas exploration and supply company also noted that UNC promised about 18 months ago not to buy any Texas International stock for at least two years.

That promise was made, Texas Internationa said, after it provided UNC with details of the operations of Phoenix Resources Co. Texas International owns 51 percent of Phoenix, which in turn owns oil and gas reserves in the United States and Canada.

Texas International once planned to sell its share of Phoenix, but announced this month that it was shelving the plan because Canadian tax laws made it unattractive.

Acquisition of Texas International would expand UNC Resources' energy operations in the petroleum business. UNC has a small oil company of its own, but its principal subsidiary is United Nuclear Corp., which mines and processes uranium and works on nuclear power plants.