UNITED NATIONS, Sept 21 (Louis Charbonneau/Reuters) - The Palestinians -- despite firm U.S. and Israeli opposition -- will give the U.N. Security Council some time to study their application for full membership in the United Nations, a senior Palestinian official said on Wednesday.

He also said the Palestinian delegation would politely reject U.S. President Barack Obama's demand in his U.N. General Assembly speech on Wednesday that the Palestinians drop their bid for membership in the United Nations, a plan that is doomed to failure if Washington keeps its promise to veto it.

We will give some time to the Security Council to consider first our full membership request before heading to the General Assembly, Nabil Shaath, a senior official in Palestinian President Mahmoud Abbas' Fateh party, told reporters on the sidelines of the U.N. General Assembly.

Some U.N. diplomats and officials have said that the 15-nation Security Council might buy time by dragging out its review of the Palestinian U.N. membership application, which Abbas has vowed to submit on Friday to the U.N. chief Ban Ki-moon.

That review, they say, could theoretically take months, or even years.

Any delay will be part of the procedure, Shaath said, adding that if there was an undue delay, the Palestinians would turn to the General Assembly.

By turning to the General Assembly, Shaath was referring to a second U.N. option the Palestinians have been considering alongside full U.N. membership.

The second possibility is the so-called Vatican option, under which the Palestinians would seek status as a non-member observer state in the United Nations, which would enable them to join the International Criminal Court and sign other international treaties and covenants.

The Palestinians are currently an observer entity at the United Nations.

It would not be difficult for the Palestinians to gain non-member state status, like the Vatican, as it would not need Security Council approval and would require only a simple majority approval in the 193-nation General Assembly. It would also be an indirect recognition of Palestinian statehood.

Full membership requires Security Council approval and a two-thirds majority in the General Assembly.

Shaath said Abbas would make all of this clear to Obama when the two meet in New York at 6 p.m. eastern time (2200 GMT).

When we meet President Obama we will re-explain our issue, why we have to have United Nations membership, Shaath said.

We will really cordially and respectfully tell him 'No'. We are insistent, he said. This is morally, politically, and legally correct what we are trying to: joining the United Nations.