U.N. Ambassador Jeane J. Kirkpatrick, considered by government officials here to be an influential channel to the White House, arrived today, and the Salvadoran leadership pressed its case for more U.S. aid in the war against leftist guerrillas.

Kirkpatrick, on a tour of Panama, Central America and Venezuela, is regarded here as champion of this government's stand against negotiations and its determination to extinguish the leftist challenge militarily. Foreign Minister Fidel Chavez Mena hailed her on arrival as "an extraordinary woman" defending "the noble cause of the Salvadoran people."

Kirkpatrick, who is scheduled to go on to Caracas Friday for her final stop, portrayed her tour as a follow-up of President Reagan's trip to the area late last year and said it was requested by Reagan and Secretary of State George P. Shultz.

El Salvador's armed forces have suffered serious reversals in recent weeks at the hands of guerrillas from the Farabundo Marti National Liberation Front, and the government and its U.S. advisers are urging more aid to handle the increased rebel threat.

"The lady, with her preparation, [will have] better vision and will be able to translate to President Reagan with increased clarity the internal situation this country is passing through," Chavez Mena said, adding that he plans to bring up Salvadoran pleas for more aid in his talks with Kirkpatrick. He said the government judges military aid should be increased "substantially" from the $26 million allotted for 1983. U.S. military advisers here, who had requested $60 million for that period, have warned that the current level endangers the Army's chances against the increasingly aggressive guerrillas.

The Reagan administration is seeking $86 million for next year. But Chavez Mena apparently was referring to hope for an emergency injection of aid for this year, similar to the $55 million provided above regular levels last year to replace Air Force planes blown up in a raid by the guerrillas. He said the aid level should rise "at least" to the $60 million requested by the administration but shaved back to $26 million in a continuing resolution at the close of the last Congress.

Thomas O. Enders, assistant secretary of state for Inter-American affairs, told Congress last week that such increased military aid may be necessary in the light of recent military developments favorable to the guerrillas. Some reports have suggested the administration also was considering dispatch of more U.S. military advisers, raising the current ceiling of 55.

This would be particularly delicate in Congress now. An adviser was wounded last week while flying in a U.S.-provided helicopter over a guerrilla roadblock. Three advisers were sent home two days later, after the embassy said they were involved in tactical missions against guerrillas. An understanding with Congress forbids advisers from accompanying Salvadorans in combat.

An increase in advisers would permit them to be present at the brigade and provincial command levels, where they could encourage Salvadoran officers to employ the small-unit patrols that the Americans say are essential to defeat the guerrillas.

Stationing advisers at lower command levels also could expose them to combat situations, however, making the idea difficult politically.

Gen. Wallace Nutting, commander of the U.S. Southern Command based in Panama, and Nestor Sanchez, deputy assistant secretary of defense for Inter-American affairs, testified in Congress last week that the recent guerrilla victories were due in large measure to the Salvadoran Army's tendency to mount massive sweeps rather than such repeated patrolling.