The thicket of trees still blooms in the 11-story atrium lobby, the parquet floors are still waxed to a high gloss, and the grant checks still go out on schedule. Nevertheless, these are sad days at the $2.8 billion Ford Foundation.

Robert Schrank, who is retiring voluntarily after 10 years as a program officer at the foundation, described the current level of activity as resembling Sleepy Hollow, and the mood equivalent to that of an undertaking parlor.

At a time when the Reagan administration is cutting funds for domestic social programs and many look to private giving to take up the slack, the nation's largest foundation is in disarray.

Two years after becoming the first black to head a major foundation, Ford Foundation President Franklin A. Thomas is facing a degree of criticism and invective almost unprecedented in the genteel world of major philanthropy.

"I see myself as having been asked to lead the foundation out of what has been described as a period of draft and indecision," Thomas said in a recent interview.

Although disturbed by "the personal nastiness" of the attacks on him, Thomas sees them as a predictable response to his efforts to bring tighter management to the foundation. He is particularly proud of a six-part thematic agenda, announced in April, that he said he believes will help Ford "regain control over its own strategic planning."

When the foundation's trustee held their quarterly meeting 10 days ago, Thomas underwent what one trustee called "very blunt" questioning on a series of mass firings known in the corridors of the foundation as the "May Day Massacre."

Thomas, 47, who succeeded McGeorge Bundy in 1979 after commpiling an exemplary record running an antipoverty program in Brooklyn, retains the trustees' support, but his executive abilities have been questioned.

"Thomas' problem is that he has no depth of experience in managing a large institution," board member Irving S. Shapiro said.

The victims of the so-called massacre in mid-May were most of the remaining Bundy-era program officers. More than 25 of these grant managers, with salaries ranging from $35,000 to $70,000, were terminated.

Thomas, who calls the dismissals an "unpleasant, wrenching experience," delegated to others the task of notifying the program managers that their contracts would not be renewed.

The purge sent shock waves through New York's philantropic community, where the Ford Foundation is the trend-setter. As a high executive of another leading foundation put it, "I don't even know who to talk to at Ford now. Domestically, we've held up several things pending what Ford is going to do."

An aura of secrecy traditionally surrounds the inner workings of the Ford Foundation because of a strong sense of innstitutional loyalty among the staff and a potent old-boy network that rewarded former employees with grants and lucrative consulting contracts.

Now, as departing program officers wind up their affairs and make copies of their resumes, they have lost their normal inhibitions about laundering the foundation's dirty linen in public.

Nevertheless, undefined fears of retribution make them reluctant to speak for attribution. "I still have my career ahead of me," said na ousted program officer who requested anonymity. "Frank Thomas is not one to take security leaks lightly," said a Ford staffer who was retained.

Many complaints about Thomas are rooted in fact. He did trade in Bundy's Ford Torino for a Lincoln Continental. Ford staff members once could see Bundy with his feet up on his desk in the president's fishbowl-like office. Now all they can see are venetian blinds and a screen of five plants installed by Thomas.

It is universally agreed that Bundy ran the foundation like a college faculty, while Thomas' style is more that of a corporate executive. This has caused difficulties at Ford, where even some of Thomas' supporters describe him as inscrutable.

Robert W. Chandler, one of the fired program officers, complained that Thomas "didn't give any clear signals." A Bundy-era progam vice president observed that "Thomas finds it very difficult to delegate and very difficult to communicate. Everything is a one-sentence announcement."

Four of the purged program officers, including Chandler, ranging in age from 56 to 62, have filed age-discrimination suits with the Equal Employment Opportunity Commision. The EEOC suits are a particular embarrassment to the foundation's board, given the instituation's long history of civil rights activism. Board member Sharpiro described the law-suits as "a source of pain."

Thomas defends his actions as part of a "slimming down and restructuring" of the foundation. "You could wipe out 98 percent of the negative comments if I decided to work an eight-hour day instead of a 14-hour day and to enjoy the position instead of taking on leadership responsibilities, he said.

During his first 18 months in office, Thomas moved slowly, prompting concern at a board meeting in December, 1980, about the pace of change. Part of the delay may be due to Thomas' heavy outside responsibilities, which include six corporate directorships and, until recently, chairmanship of a Rocketfeller Foundation study on southern Africa.

This year, Thomas has moved aggressively to place his personal stamp on the Ford Foundation.

He gingerly removed the five program vice presidents inherited from Bundy, and clipped the power of the once semi-independent international division. In March, with much fanfare, he announced his long-awaited thematic agenda for the 1980s. He also beat an attempt by the manager of the foundation's investment portfolio to establish an independent management affiliate on the model of Harvard University.

Each of these steps has mobilized Thomas' critics. Many in the foundation world note that his two new program vice presidents lack the stature of their predecessors.

One former Ford vice president dismissed Thomas' thematic agenda by saying, "There is nothing new in the themes." After reading the themes and meeting with Thomas, the president of another large New York foundation said, "I still do not know where the Ford Foundation is going."

A Ford trustee complained that there was "an unfortunate amount of turf protection" in Thomas' refusal to allow the foundation's portfolio management to leave his direct control. The fight prompted the resignation of Jon L. Hagler, the highly respected portfolio manager. The trustee called Hagler's departure "one of the worst things that has [happened] and can happen to the foundation."

When he succeeded Bundy, Thomas had a mandate to clean house. Board member Donald S. Perkins said, "The feeling on the part of many trustees was that the foundation needed more management."

This concern with management, particularly keen among activist businessmen on the board, stems from the 1974 stock market decline that wiped out almost half of Ford's assets.

Under Hagler, the investment port-folio made a strong recovery, but the current $102 million program budget, adjusted for inflation, is now only about one-fourth of what it was in the early 1970s.

"The institution's resources had changed enormously, and the style of operation was no longer appropriate," Thomas said in an interview. Thomas was careful not to criticize his prodecessor directly, but he provided hints that he was alarmed at the vagueness, the old-boy network, the paternalism toward grantees and the top-heavy bureaucratic structure that he said he believes characterized the foundation under Bundy.

"I want to know why we have so many ex-staff members working as consultants for 100 or 200 days a year," Thomas said. He also noted that there are those who "behave as though the purpose of this institution is primarily to preseve the jobs of the people who work here."

Money clearly was one reason for the mass firings, even though under termination agreements, which Thomas called "generous," all are still working at the foundation and many will be paid until next year.

Board member Perkins said that "The choice was between staff or grants." Only half of the terminated program officers will be replaced. Foundation Vice President Alvin N. Puryear said many of the new staffers will be hired at salaries between $30,000 and $35,000.

Thomas' supporters described some of the fired program officers as "deadwood," but none would defend the way the terminations were handled. Board member Rodrigo Botero was typical when he called the firings "regrettable," and added his wish that "it could have been handled differently."

Some of those terminated, like civil rights attorney R. Harcourt Dodds, had expected a promotion, not a dismissal. Dodds' situation is particularly ironic, since he first met Thomas in the early 1960s, when both were young federal prosecutors in Manhattan.

"I helped Frank learn to track cases and taught him the ropes," Dodds said, still puzzled about the lack of an explanation for his firing.

Morale has plummeted within the foundation's steel-and-glass headquarters on 43rd Street in Manhattan."No one wants to work," said one of the retained program officers. "It's really hard each morning to walk from the train station to the foundation in an atmosphere like this."

The firings have produced some surreal moments. One week after the purge, more than 20 of the ousted program managers dutifully filed past Thomas and board Chaiman Alexander Heard on the receiving line at a party for retiring education Vice President Harold Howe II. This being the Ford Foundation, there were no harsh words or angry scenes, just strained expressions. But one participant described the party as resembling a Fellini movie.

Despite the turmoil, the foundation continues to go about its business of giving away money. Last month at the board meeting, the trustees approved Thomas' two-year, $240 million program budget, at the same time rapping his knuckles over the firings and warning him, in the words of one trustee, "not to pull this stuff again."

The budget, which is being increased by 17.6 percent, provides tangible clues to Thomas' priorities. Funds to fight urban poverty have been increaded 75 percent, and spending international for human rights programs will double.

The major loser in the two-year budget is the arts, which had long-standing support. Pending a further board review, funds for the arts have been sliced from $8 million to $2.1 million.

The new budget is designed to showcase Thomas' six new programmatic themes, which cut across the traditional divisions between domestic and international programs. But many within the foundation grumble about the haste with which this thematic structure was assembled.

In January, after the board helped goad him into action, Thomas organized the foundation's program staff into seven "theme teams" to develop 10-page papers to submit to the trustees. Three of the team leaders, including Dodds, were among those terminated in May.

According to many participants, the frenetic preparatin of these papers, with first drafts produced in one week, compromised their quality. Thomas E. Cooney Jr., one of those who have filed EEOC suits, said, "The general feeling was that the process was too hurried, too cut-and-dried and too limited to develop new ideas or even creative restatements of old ones."

In March, the board winnowed these papers to six themes, eliminating one on youth and sending back the paper on higher education for more staff work. This mandate may be hard to carry out, since everyone who has worked in higher education, an area of longtime foundation interest, has been terminated or is leaving voluntarily.

Thomas acknowledged that he is going through "a very tough process" but expressed surprise at the degree of the reaction triggered by the firings.

As one former Ford Foundation official, now a college president, put it:

"It's very hard to leave Ford. You live in that glass palace, you're paid well. It's like being at the top of a federal agency without any of the responsibility or the bureaucracy. Nobody wants to leave that place. They all want to grow to become old philanthropoids and die.