Dean Anderson, the number two official at the Smithsonian, abruptly resigned his post yesterday, citing impending financial problems at the institution that are likely to lead to "program reductions or even terminations, likely accompanied by restructuring of the current organization."

In a letter dated yesterday to Smithsonian Secretary Robert McC. Adams, Undersecretary Anderson, 43, suggested that "a fresh perspective may be helpful in making hard decisions on downsizing." Adams appointed Nancy Suttenfield, director of the Office of Planning and Budget, to serve as acting undersecretary when Anderson's resignation becomes effective Sept. 1.

Adams released a statement in which he accepted the resignation "with regret" and expressed appreciation for Anderson's "17 years of dedication to the Smithsonian exemplifying the highest standards of public service." Anderson, who will become senior adviser to Adams effective Sept. 2, is out of town and could not be reached for comment.

In his capacity as undersecretary, Anderson serves as a liaison between Adams and the senior staff and oversees day-to-day operations.

Several Smithsonian officials confirmed that money has been a dominant concern in recent months. Tom Freudenheim, assistant secretary for museums, said he and others have been conducting reviews in anticipation of possible deep budget cuts in fiscal 1991. "We have been told that we need to be ready for '91 numbers that may be lower than we anticipated," he said. " ... I haven't been mandated numbers. All I've dealt with was looking at program issues and trying to make program priority judgments."

Freudenheim said officials at the institution "are very concerned and very worried with the kinds of priorities that people have." So far, he said, no decisions have been made and the discussions have been kept "extremely confidential." Normally, he added, "papers get passed around broadly," but that has not happened in these financial discussions.

Freudenheim said he was surprised and saddened by Anderson's decision. "I was shocked. It wasn't expected," he said. He said Anderson's departure means that "somebody with just enormous competence is not going to be there. Institutions, fortunately or unfortunately, survive... . People are more fragile than institutions."

While acknowledging the general money concern, Freudenheim said he knew of no specific decision or incident that triggered Anderson's departure. Other officials were equally surprised and baffled. Robert Dierker, deputy assistant secretary for media, said in a statement, "I think it's fair to say that this place is in shock and that the absence of a conspicuous, plausible reason is making a whole lot of folks around here feel pretty insecure at a time when our financial pressures demand cohesion, not distraction."

Dierker said Adams's decision to accept Anderson's resignation "is not likely to rank historically as highly as his visionary decision to hire (promote) Dean in the first instance." Adams tapped Anderson as undersecretary five years ago.

Smithsonian spokeswoman Madeleine Jacobs said Adams "has been talking to the entire staff since early June about tight budgets and hard times ahead. We have been looking very hard at all our programs." Adams has also been discussing a possible management restructuring with the board of regents "for some time," she said. Jacobs said the discussions are highly confidential. As for Adams's specific plan for management restructuring, she said, "He hasn't shared that widely." She said Anderson "has felt for some time that the institution is changing."

In his letter of resignation, Anderson said "an extraordinary boom was afoot" when he started at the Smithsonian 17 years ago. "I had the pleasure of helping to bring on a steady procession of new bureaus, from the Hirshhorn to the Museum of African Art; from the Cooper-Hewitt to the Sackler; and I enjoyed thinking through and helping establish our Collections Acquisition Program and Special Exhibition Fund. Steady growth seemed inevitable," he wrote.

Anderson said he owes Adams "the opportunity to select a new Under Secretary to assist you with the distinctly different and trying tasks ahead -- someone whose skills are more in line with impending challenges. While I have confidence that the Institution can come through with its basic strengths intact a fresh perspective may be helpful in making hard decisions on downsizing while continuing to seek new opportunities to fulfill its mission."

Adams's nearly six-year tenure at the Smithsonian has had its share of controversy. Last spring, 22 of the institution's 67 museum and office directors told Adams they were "troubled" by what they described as "a proliferation of staff positions at the management level that as yet seem to contribute to, rather than improve, the confusion." Recently there has been controversy over the extent to which the Smithsonian permits corporations to underwrite exhibitions.

The Smithsonian is made up of 15 museums and galleries and the National Zoo. Its 1991 budget request totals $307.7 million. The 1990 appropriation was $266 million. Its total 1990 budget of $353 million includes federal funds, government grants and contracts, and revenue from trust funds.