U.S. Ambassador to Nicaragua Lawrence Pezzullo today joined Ambassador to El Salvador Robert White in accusing persons claiming to represent the Reagan transition team of undermining their authority in Central America and worsening grave crises.

In unusual on-the-record statements by telephone from Managua, Pezzullo, a career diplomat who is in his second ambassadorship, said leaks from the team of President-elect Ronald Reagan on proposed policy, and visits here by people allegedly portraying themselves as Reagan's emissaries, "undercut you in the midst of a delicate situation.

"It is disturbing, and I don't think it serves the transition, and I don't think it serves Reagan," Pezzullo said. "It's certainly not a smooth way to take over the reins. I feel sorry for Reagan." He said the president-elect "should have the best professional advice because of the sensitivity of the area."

In another recent conversation, Pezzullo said he fears that the right wing of the Republican Party may force the Reagan administration to "feed" it by letting it "eat up Latin America. It's cheaper than some other places like the Middle East, the Soviet Union or China, where no president is going to have much room for radical policy changes."

The immediate cause of White's and Pezzullo's outrage is a reported "hit list" prepared by Reagan advisers naming envoys for immediate removal as liberal "social reformers." White and Pezzullo were on the list. Robert Neumann, head of Reagan's State Department transition team, could not be reached for comment today. Earlier this week, however Neumann said the "hit list" published after it was leaked last week, was only a "first cut" draft composed by individual team members and was neither policy nor even a recommendation that would necessarily be passed on to Reagan.

Neumann and other transition team members also denied having sent Cleto Di Giovanni Jr., a former CIA officer with ties to the team, as an emissary to Central America last week. Di Giovanni also denied in Washington that he had portrayed himself as representing Reagan.

Pezzullo said that Di Giovanni had shown up in Nicaragua, as well as El Salvador, last week and had met with a number of people as a Reagan emissary, and that he is not the only person to have done so in the last several months.

"This has been going on for a long time and for the Reagan people to say now that 'these guys don't speak for us' is kind of lame," Pezzullo said. "I don't buy that for a second."

Both White and Pezzullo say they fear that delicate political situations in the region will be upset by spreading reports that Reagan will support a right-wing takeover in El Salvador and will seek to drive the leftist Sandinistas from control in Nicaragua.

More important, Pezzullo said today, he feels the regional situations will move so rapidly on the basis of such reports that Reagan will have few options by the time he is inaugurated.

The Republican Party platform, and numerous Reagan spokesman, have said they believe the Nicaraguan government is Marxist- and Cuban-controlled. They have called for an end to the Carter administration policy of supporting the Sandinistas.

On El Salvador, Reagan officials have said they believe the military should be strengthened to quash a leftist threat, despite widespread reports that the military itself is engaged in repression and murder against the civilian populace.

White said on Tuesday that interference from Reagan advisers and hangers-on who claim to speak for him has seriously increased the chances of out right civil war in El Salvador, where the administration has supported wide-ranging social and economic reforms in an effort to diffuse the appeal of the left.

White and Pezzullo are veteran foreign service officers -- Pezzullo has served under every administration since Dwight D. Eisenhower -- which decades of experience in Latin America. Both indicate they have put their immediate futures on the line by speaking out.

They characterize the current situation in Latin America as requiring pragmatism and not doctrinaire posturing.

Pezzullo said in a coversation several weeks ago that he agreed today to put on the record, "This is a new administration. There are going to be some tradeoffs" that will allow the Reagan "right-wing" a relatively free hand in Latin America.

"That's the way I tend to think things will go," Pezzullo said. "Just feed the area to the lions."

"To think that the extreme right is the solution down here is lunacy," Pezzullo said today. "To think you can go back to the policies of the past is lunacy."

Pezullo charged crucial mistakes in Central American policy to the Nixon administration when he said opportunities for peaceful reform were largely ignored.

The ambassador cited the 1972 elections in El Salvador when a victory by the moderate opposition was voided by the ultra-conservative military. The loss of faith of the Salvadoran people in the electoral process and the radicalization that has fueled powerful Marxist guerilla movements here are widely alleged to date from that electoral fiasco about which the United States said and did virtually nothing.

In the meantime, another diplomat charged recently, a succession of weak and ineffectual U.S. envoys -- many of them political appointees -- were sent to the area.

"It's sad," said the diplomat, speaking of the pressures currently being put on his colleagues. "I can't remember when we've had more first-rate people here. Before, we really had some of the dregs. You had some people around you wouldn't bring into polite company. The United States was not paying attention."

The situations of Nicaragua and El Salvador are going to demand very close attention in the next few months, White and Pezzullo say, if the United States is to avoid getting into very deep trouble.

In the case of El Salvador there is a serious risk, underlined by the murder of five prominent leftist leaders and four American churchwomen in the last two weeks, that the country will erupt in full-scale war.

Already the government here that the Carter administration nurtured for 14 months is in a shambles due in part to right-wing pressures.

"If the military chooses to break up the government under these various pressures and try to reverse the reforms that have taken away the left's ability to mobilize the great masses of people they formerly could," White said Tuesday, "then what you will see is the left fueled by new adherents."

In Nicaragua, Pezzullo said, the United States had to make the best of what was initially a very bad situation from Washington's point of view after the victory of the leftist Sandinistas in July 1979 over dictator Anastassio Somoza. "We salvaged what was an absolute disaster," Pezzullo said. "I don't think we could have played our cards any harder. You talk to anyone in this town and the American Embassy is respected."