At least a third of the members of the presidential commission investigating the Three Mile Island accident want to recommend that President Carter break up the Nuclear Regulatory Commission.

Sources close to the commission said that no fewer than four of the 12 members want to strip the NRC of its licensing and emergency planning powers, handing the licensing function to the Environmental Protection Agency and emergency planning to the new Federal Emergency Management Agency. The latter was established after the Three Mile Island accident last March threatened to force the evacuation of 250,000 people from the Harrisburg, Pa., area.

"There's a feeling among the members that one reason the accident happened at TMI is that the NRC spends too much of its time on licensing instead of regulation," one source said. "Some members feel the NRC simply does not spend enough of its time regulating and enforcing its rules."

Should the commission recommend it and the White House act on it, the stripping of licensing and emergency planning functions would leave the NRC with the power to regulate operating nuclear plants in the United States. The NRC would also still retain the power to ban or allow exports of uranium, a function mandated by Congress.

The NRC has had those powers since January 1975, when the old Atomic Energy Commission was broken up into the NRC and the now-defunct Energy Research and Development Administration.

While the commission is nowhere near the point of making recommendations to the White House, its staff is in the process of drafting some 240 "findings" to be placed before the panel when it meets here next week. One of the first orders of business then will be to sort through the findings and decide which are unimportant and which significant ones can be combined with others.

But even before the commission does that, sources said, it is debating what kinds of recommendations it wants to make to the White House about the future role of the NRC.

The panel, known as the Kemeny Commission after chairman John G. Kemeny, is considering a recommendation to scale down the five-member NRC to a single member who would be chairman and chief executive. Currently, decisions are sometimes split and are often delayed and watered down by debate.

"Right now, the [Kemeny] commission is split on that subject," one source said. "We know the pros and cons of having a single head and the pros and cons of having five commissioners and I don't know where we're going to come out on this one."

Sources said Kemeny Commission members feel far more strongly about stripping the NRC of its licensing function than they do about changing it over to one-member rule. While four of the 12 members were described as active supporters of a breakup of the NRC, none of the remaining eight were described as being in active opposition to a breakup.

Sources said that half the commission members "feel strongly" that the NRC spends too much of its time on the procedures that lead to the licensing of a nuclear power plant, a process that takes as much as six or seven years.

"Once a plant gets its operating license," one source said, "there is a tendency to forget that plant. The regulation of that plant then becomes quite lackadaisical."

At the same time that licensing gets too much attention, sources said, some panel members think the regulation of nuclear plants and the enforcement of the rules that guide regulation get too little attention. One source described the NRC'S Office of Inspection and Enforcement as a "stepchild" casino -- a rumor on which he will not comment.

"I agree with that description," another source said, "although it's not at all clear why it has become a stepchild."

Next week's meetings of the full commission will run for three days. At least one more meeting will be held later, probably the week after.

President Carter has told the commission he wants its recommendations Oct. 25, a schedule that insiders say is now tight but can probably be met. By law, the commission will exist another two months after making its recommendations, being dissolved on Christmas Day.