President Carter's energy program is the product of intense secretive work by a tight circle of officials who drew heavily on ideas and statistical models inherited from the Ford and Nixon administrations, according to those involved.

The pace of work was so hectic and the desire to maintain secrecy so intense that many basic decisions about the program were not made until the last day or two before it was announced Wednesday night. Even yesterday the administration could not confidently estimate the program's potential impact on the economy - a subject the energy planners did not consider seriously until the last fortnight.

Some details of how new energy taxes will bve rebated to the public also remain to be worked out.

As late as last weekend, Carter personally was still agonizing over the fact that the energy plan did not include total deregulation of newly discovered natural gas. In his campaign Carter had advocated such deregulation, and "he takes those campaign pledges very seriously," one associated said.

The authours of the plan, who are proud of it, describe the process that produced the final documents as frenetic, difficult, but in the end extraordinarily successful.

The April 20 deadline imposed enormous pressure, but it was "a good thing," according to S. David Freeman, one member of the tight circle around chief energy adviser James R. Schlesinger who helped write the plan.

Without the deadline, Freeman said in an interview, "we could easily have spent the summer and fall [drafting the plan] and come up with a watered down project" that would have been "nickeled and dimed to death" in protracted bureaucratic and political bargaining.

Outsiders who have watched the process members of Congress and their staffs, interested lobbyists and others - agree about the freneticism, but not necessarily about its alleged benefits. "They got off to slow start, then set an unrealistic deadline," according to one congressional source, "and the President's program reflects the haste with which it was put together."

Interviews in recent days with numerous government officials and interested outsiders leave these impressions about the Carter energy program:

It was produced by a small staff assembled bu Schlesinger. They worked in secret, denying other federal officials and outsiders access to their most important deliberations. In the last few weeks, senior officials of the Treasury, the Office of Management and Budget, the Council of Economic Advisers and the National Security Council had to apply "tremendous pressure" on Schlesinger to get to see a draft of his proposals, according to one well-placed source.

These senior officials wanted to see how the energy plan would affect areas of interest to them, particularly the overall economic situation. Schlesiinger, however, felt that the plan would be diluted or distorted if other agencies got a shot at it before the President had decided on its principal ingredients.

Schlesinger elicited decisions from Carter by sending him a steady stream of options papers during recent weeks. Each paper contained "blocks" of issues for a presidential decision - from five to 18 different issues at a time, according to one source.

The options Schlesinger offered his boss were produced by the staff of Pentagon veterans, energy experts and new associates who put in long hours in the makeshift energy offices in the Old Executive Office Building. "It's really just been an endless day," Freeman, one of Schlesinger's associates, reflected on the past 90 days. Freeman worked until 5 a.m. Wednesday - the day Carter unveiled his program - on a final fact sheet for the press.

The plan that Schlesinger and Carter agreed on survived relatively intact through a marathon Cabinet meeting that began April 6 and continued intermittently over that next two days. However, under pressure from economists and others, some of its harsher provisions were watered down.

Schlesinger also feared leaks to the press, which also accounted for his staff's secrecy. In early April - within days of the first circulation of draft proposals in the government - details of the drafts were published in The Washington Post and the Wall Street Journal.

The secrecy and urgency with which the energy program was drafted probably resulted in some errors and oversights, but they also enbled the President to fulfill his pledge to produce a dramatic, comprehensive program in a brief period.

Apparently, Schlesinger and his associates still cannot explain the dollar costs of their proposals to individual Americans or the national economy.

Plans to explain the program in a detailed background book - intended to be released Wednesday - were abandoned last weekend. "You never saw such a mess," said one official who was supposed to help prepare that book.

Late last Friday night, Under Secretary of Health, Education and Welfare C. Hale Champion received an urgent request to help the White House calculate the impact of the energy program on poor people. Champion spent much of last Saturday at meeting devoted to that subject.

If Schlesinger's burgeaucratic method produced confusion, however, it also produced results.By assembling a new staff and avoiding the bureaucracies. Schlesinger defied the conventional wisdom of bureaucratic Washington, completing an ambitious examination of energy options in what must be record time for such a large undertaking.

The Carter plan draws heavily on statistical models and ideas produced during the Nixon and Ford administrations, and on the expertise of many past energy officials.

Carter has adopted one basic priciple from Ford: that energy must cost more if people are to be persuaded to use less, and producers are to tbe induced to find more. Carter rejected a free market in energy, but the proposed tax and price adjustments that will raise energy costs - and energy industry earnings - by billions.

However, Carter's combination of proposed new measures is original, and his emphasis on conservation rather than expanding energy supplies is a marked departure from the previous Republican administrations.

"There's been a lot of work [on possible energy programs] for the last three years... exploring what the options are," according to one participant in the policy-making process. "There are only so many options," he added, "so there are a lot of similarities" between the Carter plan and previous approaches.

The Federal Energy Administration's computer model - known as the "Project Independence Evaluation System" - was one of the basic tools the Carter administion inherited. The PIES computer can project the impact on production consumption and other energy variables of various government actions.

However, the new administration was willing to adjust the PIES numbers if it felt they were unjustified. For example, in his fireside chat President Carter predicted that without a new energy program, the United States would be importing 16 million barrels of oil a day in 1985. The PIES projection for that statistic is 12 million barrels a day, but this was altered on the grounds that the PIES assumptions were probably too optimistic.