Secretary of State Alexander M. Haig Jr. flew here today for talks with King Hassan II against a background of persistent Moroccan appeals for increased U.S. support against the Polisario guerrillas in the Western Sahara.

A senior U.S. official accompanying Haig said there is nothing "dramatic or urgent" about the visit. He said Haig, who attended a conference in Madrid earlier this week, was taking advantage of his proximity to Morocco to make up a December trip that was canceled because of the Polish crisis.

The official also acknowledged that the Reagan administration places a premium on cultivating close ties with Hassan because he is an important moderate among Arab leaders and Washington views him as a potentially key ally in furthering U.S. diplomatic and strategic goals in the Middle East.

The senior official said final amounts have not been decided but the administration plans to ask Congress for "a substantial increase" in military assistance for Morocco, which currently is pegged at $34 million in military sales credits for fiscal 1982.

In addition, the official continued, Morocco is among those countries to be included in a new administration bid to convince Congress that it should grant the aid on either at an unusually low interest rate or forgive part of the amount that must be repaid.

In Morocco's case, this is especially important because Hassan's government is so strapped financially that it has been unable to accept Washington's offer to sell 108 M60 tanks at current terms.

There have been recurrent rumors that the United States, in exchange for increasing its aid, wants to win Hassan's permission to reopen one or more of the four Moroccan air bases maintained by U.S. forces until 1963. The official acknowledged the possibility of seeking landing rights in cases where a crisis might require use of the evolving U.S. Rapid Deployment Force.