Energy Secretary Charles Duncan defended his department's efforts to spur conservation and development of solar energy yesterday but didn't respond directly to critics who claim the administration isn't spending enough money to meet its own goals for either.

Citing President Carter's committment last year "to derive 20 percent of all the energy we use from the sun" in the year 2000, Rep. Richard L. Ottinger (D-N.Y.) told Duncan at a House Science and Technology subcommittee hearing, "The record of the past year, and the prognosis for the future, has been an immediate and continuing betrayal of this commitment."

Ottinger said recent studies by the General Accounting Office, Congress' Office of Technology Assessment, as well as the Department of Energy's own conservation and solar energy division, all indicated "the level of funding is far below that needed to achieve the goal."

Duncan, in reply, stressed his department's recent creation of a "dynamic and flexible management process" for handling support of conservation and solar programs. And at one point, he noted that, as a manager, he is forced to make "difficult decisions" about how best to use the resources available for all DOE programs "in a time of budget restraint."

No member of the subcommittee ever specifically asked the energy secretary whether present spending levels are adequate to meet President Carter's announced goal, and he didn't volunteer an answer.

Duncan took strong exception, however, to a report issued this week by the Office of Technology Assessment that declared: "There is a pervasive belief within and outside of DOE that senior DOE management does not really care about the (conservation and solar energy) programs. . . ."

When Rep. Allen E. Ertel (D-Pa.) questioned why DOE wasn't doing more to promote energy conservation, Duncan heatedly reported, "Maybe you need a new secretary.

"I personally am doing as good a job on conservation as I know how," he continued, describing a number of things he has done and changes he has made within DOE to push conservation. "It is very unfair and very unrealistic to assert the opposite, as the OTA did," he said.

The hearing was called after recent publication of internal DOE planning documents indicating funding for various solar energy technologies -- which include wind, wood, hydroelectric and other such energy sources as well as more conventional solar devices -- wouldn't increase during the 1982-to-1986 period as much as backers of solar wish.

Spending for other programs, such as for oil shale commercialization and nuclear reactor research, would rise faster than planned earlier, according to the documents.

Another memorandum sent in March by DOE's conservation and solar energy division to Duncan -- excerpts of which were distributed at yesterday's hearing -- declared, in part: "By setting the 20 percent goal, the president indicated that the country needs to make renewable resources an important source of energy by the end of this century. However, the (fiscal) '80 budget (for the year ending in September) did not rise above a business-as-usual level in response to that new commitment. Again, a year later, the FY'81 budget shows no marked increases."

The DOE memo continued, "The 1982 budget should show a sizable increment to solar funding over the previous budget or at least include analysis that demonstrates that a continued low level of funding is consistent with the 20 percent goal.

"Existing analysis does not indicate the latter," the DOE memo stated. "Rather, it shows that for each technology, the basic level (of spending) is is far below that level of funding that could realistically lead to attainment of the 20 percent goal."

Duncan, obviously miffed that the internal documents had been leaked to Congress and the press, said comparing funding levels alone for various energy alternatives could lead to an "improper conclusion" about the degree of commitment the administration has to a particular approach.

The cost of a single large plant to demonstrate the commercial feasibility of making liquid or gaseous fuels from coal could take far more money than a large number of equally useful demonstration projects for solar technologies, which by their nature can be far smaller and still provide the needed information, Duncan said.

The energy secretary also pointed out that spending on solar energy five years ago was only $40 million. By 1978 that had jumped to $500 million and will be about $1.1 billion this year and $1.4 billion next year, if tax incentives for individuals and businesses to install solar equipment are included.

With homeowners now able to get a 40 percent tax credit and businesses 25 percent for such installations, and DOE planning to spend about $690 million on various solar projects in 1981, Duncan said there is "a strong federal commitment to solar energy, and I expect that commitment to continue . . ."

Rep. John W. Wydler of New York, the ranking Republican on the full Science and Technology Committee, praised Duncan for taking a "businesslike approach" in managing DOE's bureaucracy. "It has been refreshing to see this ingredient of accountability sprinkled throughout DOE, but, unfortunately, overzealous supporters of certain programs have chosen to interpret this responsible approach as an attack on their favorite technologies," Wydler said.