The Pentagon denied yesterday that military planners had warned desert sand or dust storms would jeopardize the hostage rescue mission if President Carter waited as long as April to launch it.

Thomas B. Ross, assistant secretary of defense for public affairs, issued the denial in respones to The Washington Post story of Sunday which said Joint Chiefs of Staff planners had made such a warning to Carter.

The president on April 11 gave the go-ahead for the mission, which was aborted in its first stage for lack of enough helicopters to go further. The helicopters did run into severe dust storms, but Ross said meteorological tables show April is not a prime month for them.

Ross said those tables show the incidence of sand or dust storms "goes up dramatically in May and June," while the weather in December through February is icy, turbulent and cloudy.

The mission was attempted on April 24. Ross said the history of weather for the month showed no inordinate threat from sand or dust storms along the route the helicopters took after being launched from the aircraft carrier Nimitz in the Arabian Sea.

A high military official, in briefing reporters at the Pentagon on the problems encountered on the mission, said the sand storm was so severe that one helicopter returned to the Nimitz and a second landed on the desert for a while until the worst passed over.

At the White House, spokesman Jody Powell said it was true that the longer the mission was delayed, the riskier it would become. But he said, "I do not know whether the relative incidence of sandstorms" was part of the reason for the risk increasing.

Asked if President Carter were willing to accept casualities in attempting the military rescue of the 53 hostages in Tehran, Powell declined to discuss that aspect of the mission.

In other post-audits on the rescue atempt, the House Armed Services Committee yesterday heard testimony in closed sesion from Col. Charlie A. Beckwith, the leader of the Blue Light unit, which would have stormed the embassy if the mission had gone forward.

Rep. William Dickinson (R-Ala.) said after hearing "Chargin' Charlie" that the commander "was satisfied with eight" helicopters assigned to the rescue mission "because if you add more, it takes more C130s to fuel them and makes the whole thing too cumbersome for stealth."

Beckwith has said that he recommended aborting the mission at Desert One, the refueling point in the Iranian desert, because he was down to five helicopters when the plan called for six.

Rep. Samuel S. stratton (D-N.Y.) said Beckwith had told the committee that "If we could find out where the hostages are, we should go back in and pick them up."

In elaborating on his recommendation to abort, Beckwith, according to Stratton, said that if he had proceeded to the mountain hideaway outside Tehran with only five helicopters, he would have had to leave 15 to 18 of his commandos behind.

"He said every man had several jobs to do, and he just could not figure how he could go in with 15 or 18 fewer men," Stratton said.

The Senate Armed Services Committee will hear Beckwith and other leaders of the rescue mission in a closed hearing tomorrow.