The senior presidential adviser, a veteran of those heady, in-house debates when the confidently titled "Fall Offensive" was planned, sat pondering the strategy and policy casualties it has produced so far.

"We are not in a bunker mentality," he cautioned. "But it is sort of a hunker mentality."

On budgets and taxes, and even AWACSes, President Reagan is seeing his policies come under heavy attack on Capitol Hill. And what hurts the most, the Reagan men say, is that the heaviest damage is being inflicted not by Democrats, but by their fellow Republicans--many of them philosophic allies who might just as easily have been part of the official Reagan team.

"Every day we get new numbers, and every day the deficit predictions grow higher," complains one of the Senate's most senior Republicans. He is a man who is viewed at the White House as a true Reagan loyalist, and he is that; yet he concedes privately that the recent proposals and performance of the president News Analysis News Analysis and his advisers has left him deeply troubled.

"I suppose that when you start out with smashing victories, it is hard to believe you can hit a stone wall head on. But that's what has happened."

At the White House, they are paying attention now to the rising intensity of these private congressional criticisms that are being aired within the Grand Old Party's inner circles, those interlocking rings which link the two ends of Pennsylvania Avenue in loyalty but not fealty.

Meanwhile, in these days of hunkering, the president's top-level advisers are engaging in some of their own heavy introspection--although so far it has produced no noticeable alteration--as they review their policies and the process by which they were formed.

Three senior presidential assistants converge by happenstance in a hallway of the West Wing, where the corridors of power are contoured to the curves of the Oval Office; they fall into one more discussion about how quickly things have taken a turn for the worse, and why.

After a few minutes, they continue on their separate ways. Later, one of them observes:

"We meet and talk about why this has happened, and we look around for co-conspirators. But any one of a dozen of us--the so-called senior advisers--could have averted this."

In their meetings, the White House officials talk about how the administration's interest rate and deficit predictions have been faulty, and how the resulting need for a second radical cutting of the budget has wreaked political havoc in this political town.

They talk with concern about how some of the Republicans whom they privately call "the born-again supply-siders" now are questioning whether the economy can afford the tax-cut cure they have already enacted. And they concede that they have not helped their cause in the long run with their early optimistic forecasts.

"Ronald Reagan by nature embraces the best-news predictions of his advisers, and some of the rest of us prefer looking through rosy glasses, too," says one senior White House adviser. "We were, all of us, too optimistic early on."

They also are said to talk, in some of those White House meetings, about the quality of the economic advice they are getting; and word that they are concerned has made the rounds, via those interlocking rings of Republicanism, to Capitol Hill.

These concerns, says a Senate Republican source, include the advice given by Murray L. Weidenbaum, chairman of the president's Council of Economic Advisers, and Treasury Secretary Donald T. Regan, among others. "At the White House, at the highest levels," says the source, "they have reached the conclusion that they just do not have confidence in the economic advice they are getting."

In White Houses, influence tends to ebb and flow, and right now, presidential aides say it seems to be flowing in the direction of James A. Baker III, the chief of staff.

Partly because of the nature of the problems they face, and partly because of the quality of the second-level staffing, Baker appears to others in the White House to be exercising a greater influence in the shaping of policy. As originally charted, Baker is in charge of all White House operations as well as the selling of Reagan policies in Congress, in the media, and in all public liaison efforts. Counselor Edwin Meese III is in charge of all policy formulation, presiding over the Cabinet government operations.

What is happening now is that the major Reagan policies--budget, tax, AWACS (airborne warning and control system planes)--have been shaped, sent to Capitol Hill, and have run into trouble. And at the White House, now, the most crucial meetings have become those of the legislative strategy group, which meets in Baker's office.

It is still all very collegial: Meese sits in on virtually every legislative strategy session; and one does not make a major move without consulting with the other, aides say.

But it is Baker who journeys to Capitol Hill to negotiate with Republican leaders to work out the crucial details of the budget and tax and AWACS compromises.

Baker has always had a considerable voice in the shaping of policy, but those within the White House say that in the last couple of months, he has assumed a more forceful role, beginning with his decision to argue vigorously (but not victoriously, it turned out) along with Office of Management and Budget Director David A. Stockman that larger defense cuts were needed to make the new budget package credible and to win congressional approval.

Meese is as strong and able and valuable to the president as ever, being especially attuned to the thinking of his longtime boss, Ronald Reagan. But his subordinate aides are not as strong and efficient as are Baker's, according to other White House officials and Republicans in Congress with close ties to the White House.

Included in this assessment of Meese's assistants are men who are themselves figures of considerable rank: Martin Anderson, assistant to the president for policy development, and Richard V. Allen, assistant to the president for national security.

Both are men of considerable knowledge and expertise in their fields, with backgrounds in conservative think tanks and impressive reputations in academic circles. But within the upper levels of the White House staff, neither Anderson nor Allen is considered to be a strong staff administrator.

Of Meese's subordinates, assistant to the president for Cabinet affairs Craig L. Fuller alone is rated very highly by others on the White House staff.

But the administration's dominant official in domestic policy formulation is not Meese, or Baker or Anderson, as others on the White House staff see it, but Stockman. In these times of the "hunker mentality," they say, and he has become especially valuable in sorting out alternative ways of matching cuts and revenues.

"The administration has a vicar after all," said one senior presidential adviser. "But it turns out it is a vicar of domestic policy."

Within the White House senior command, there is one other realization of just what has caused the current serious straits. And perhaps it is the most important realization of all.

The president and his advisers had assumed that their biggest battles would be their intramural ones, such as that epic struggle over defense spending that pitted Baker and Stockman against Defense Secretary Caspar W. Weinberger and, as it turned out, the president.

So, even when the president could not bring himself to make significant cuts in the defense budget, the top White House officials felt confident that the Communicator-in-Chief would somehow be able to sell it to the nation and the Congress.

"We made one major miscalculation," says a senior presidential adviser. "We didn't realize that this time around no one would be willing to even work from our blueprints."

A president's channel of leadership is broad but never deep. And the Reagan officials have come to see that by handing a Republican-dominated Congress a second huge package of politically unpalatable domestic budget cuts, the president in effect surrendered the initiative in the shaping of the budget.

Just a month or two ago, the Reagan advisers had figured that this would be the height of what they called their "Fall Offensive." But at a meeting in the West Wing of the White House the other day, one of the president's most senior advisers suggested to his colleagues that perhaps a new title is in order now.

"Perhaps," he said, "this period should become known as the Education of Ronald Reagan."