The hottest topic at the Energy Department this week was speculation over whether Secretary Donald P. Hodel might be shifted to the Interior Department if Secretary James G. Watt does not survive his latest gaffe.

On the surface, at least, the move struck many as a natural. Hodel had been undersecretary of interior before his elevation to the Cabinet 10 months ago. And during his tenure at DOE, Hodel has worked to pacify outspoken congressional and environmental critics of his predecessor, James B. Edwards.

The argument against the move might be that Hodel is only just beginning to put his own mark on energy programs. His departure also would leave a leadership vacuum in the department, since the White House's nominee to be deputy energy secretary, Danny J. Boggs, still is not on the job. * * *

HAPPY ANNIVERSARY . . . The department has been in business six years as of today, but no observances are planned to mark the anniversary. The last secretary to take formal note of the occasion, in fact, was the department's first leader, James R. Schlesinger, who presided at a first-anniversary celebration in the departmental auditorium. ***

AND NOW, H-E-R-E-'S...The oft-postponed fourth National Energy Policy Plan, originally due last spring and later promised for midsummer, now is firmly scheduled to be unveiled next Tuesday.

Among its more interesting projections is a drop in what the Energy Information Administration expects the price of oil to be in the years ahead. Earlier this year, the 1985 price was projected to be $26.71 a barrel (in 1982 dollars). The new EIA guesstimate is $25.90. For 1990, the estimate has been slashed from $36.57 to $31.90. And the 1995 estimate has been lowered slightly from $47.70 to $46.50. ***

OUT OF OIL . . . .While the Reagan administration may have no plans to change its free-market approach to any world oil crisis, it has decided to change its leadership in that area after an emergency response test that was widely perceived as a disaster.

Ronald L. Winkler, deputy assistant secretary for energy emergencies, is out; he will be replaced by deputy assistant secretary Barton R. House, who had been on leave, attending the National War College.

Since House was a key figure in the Carter administration's oil price and allocation programs, congressional observers are wondering if the shift signals a willingness by the Reagan administration to reconsider the feasibility of relying totally on the free market in a time of crisis.

Tea-leaf readers also report that House, unlike his predecessor, will not be reporting to Assistant Secretary William A. Vaughan, who is supposed to oversee emergency preparedness. House, sources say, will report directly to Donald H. Pearlman, Hodel's executive assistant.

This is the second major program that Vaughan has lost in recent months. Operating responsibility for the Strategic Petroleum Reserve was shifted in mid-summer to DOE's Oak Ridge Operations Office, which reports to Hodel's special assistant Earl E. Gjelde. ***

NUCLEAR BUDGET IMPLOSION . . . DOE's civilian nuclear energy programs, which have been immune from the budget cuts that have devastated the department's solar and renewable energy and conservation programs, may finally get the ax in fiscal 1985.

Hodel has sent the Office of Management and Budget a $1.17 billion request for the programs, far below the $1.53 billion sought by Shelby T. Brewer, assistant secretary for nuclear energy, and significantly less than the OMB target of $1.45 billion.

Hodel achieved most of the savings by slashing the breeder reactor program--which includes the Clinch River reactor and other activities--from OMB's target of $643.6 million to $331.4 million. ***

IF YOU CAN'T BEAT 'EM . . . After two years as the department's chief Senate lobbyist, P. Thomas Cantrell apparently has decided that if you can't beat Congress, try to join it.

Cantrell has resigned as deputy assistant secretary for Senate liaison and reportedly plans to seek the House seat of Rep. James R. Jones (D-Okla.).