Grenada's Governor General Sir Paul Scoon told Secretary General Javier Perez de Cuellar by radio-telephone today that he was closing all of his country's diplomatic missions, a U.N. spokesman announced.

The call--which raised the potentially explosive issue of who represents Grenada--came after the United States vetoed a Security Council resolution deploring the "armed intervention" on the Caribbean island, to climax a 10-hour long meeting that ended at three this morning.

The phone call to the United Nations came through at about 11:30 a.m., but U.N. officials said they never established where Scoon was calling from. A U.S. mission spokesman said Scoon was calling either from the island or from a ship within its territorial waters.

In his conversation with the secretary general, Scoon maintained that he was at present Grenada's only constitutional authority but that expected elections to be held within six months.

He said nobody had a right to represent his country until a new government could be formed and he found time to appoint new diplomats to posts abroad, said the Secretary General's spokesman, Francois Giuliani. Scoon was appointed by the queen and under the Commonwealth system hence is considered the effective, if tightly limited, head of state.

The governor general agreed to Perez de Cuellar's request that his communication be sent in writing. When it is received, Giuliani said, the sensitive credentials question will be decided by the "appropriate" U.N. body. Each U.N. organ--the Security Council, the General Assembly, the various specialized agencies--makes its own decision on credentials.

Scoon's request may be challenged by the majority of U.N. members, and "we could get a Cambodia situation," said one top U.N. official. The assembly has for five years seated the representatives of the deposed government of Cambodia, rather than the one installed by Vietnamese occupation troops.

So far, the Grenadan representatives appointed by prime minister Maurice Bishop, who was assassinated last week, have maintained their legitimacy, have held a press conference, and have attended the Security Council debates.

But after American representatives challenged them yesterday in the council, the seat reserved there for Grenada remained empty, and this issue went unresolved.

However, Nicaragua and other sponsors of the resolution deploring the invasion told reporters today that they plan to bring the issue before the assembly next week. Grenada is one of the 38 delegations whose assembly credentials have not yet been submitted or approved. Last year, the credentials of its delegation were signed by Scoon.

In the council debate that ended early this morning, the resolution sponsored by Nicaragua, Guyana and Zimbabwe--which also called for the immediate withdrawal of the occupation force--was vetoed on a vote of 11 to 1, with Britain, Zaire and Togo abstaining.

Among the nations normally friendly to the United States that voted for the draft were France, the Netherlands, Jordan and Pakistan. The sponsors also were backed by China, the Soviet Union, Poland and Malta.

Before the vote, U.S. Ambassador Jeane Kirkpatrick defended the takeover as necessary to stop "an authentic reign of terror" that began with Bishop's assassination. She rejected the argument--which she called a "delusion and a snare"--that the use of force is an automatic violation of international law.

Under the U.N. Charter, Kirkpatrick said, the use of force is justified "to defend such values as freedom, democracy and peace. The charter does not require that peoples submit supinely to terror, nor that their neighbors be indifferent to their terrorization."

But her only support came from the Caribbean countries that joined in the intervention, while some 55 other nations rejected its legitimacy--some, like the British, in sorrow, but most in anger.

In the assembly, where there is no veto power, the isolation of the United States is expected to be even more pronounced.