In apparent disregard of his promise to avoid involvement in cases linked to his private law practice, Interior Secretary James G. Watt this week ordered a halt to regulatory actions that would adversely affect former clients who receive large federal irrigation subsidies in the West.

At a House Interior Committee hearing two weeks ago, Watt revealed that he intended to stop indefinitely departmental procedures that could lead to tighter enforcement of the Reclamation Act of 1902, which provides irrigation water at low cost in 17 western states.

The intention translated to action Thursday when the department officially published the delay order in the Federal Register. The order was signed by David Russell, an acting deputy assistant secretary, but announced by the department as Watt's action.

As head of the conservative Mountain States Legal Foundation, a Denver law firm, Watt appeared before Interior Secretary Cecil D. Andrus in 1977 to protest the department's proposed regulations for enforcing the 1902 law.

The principal critics of the proposed rules, drawn up the Carter administration under federal court order, are large corporate and private farmers whose holdings exceed the 160-acre limitation of the law and who benefit from the federal water subsidy.

One of the results of the Andrus-Carter proposals, if put in final form, would be loss of the federal water subidy to farmers whose holdings are in excess of acreage limitations.

During his Senate confirmation hearings last month, Watt promised to "recuse" himself from potential conflicts of interest with his private role as head of the Mountain States foundation.

Watt refused to disclose names of contributors to the foundation but told the Senate Energy and Natural Resources Committee that he would remove himself from cases touching on their interests.

Neither Watt's testimony nor questions from the committee elicited the information that he had been involved actively in the western water users' fight to stop Interior's moves toward tougher enforcement of the reclamation law.

Shortly after his nomination by President Reagan for the Interior job, Watt was congratulated by the Farm/Water Alliance, a lobby for big users of the subsidized water, and reminded of his past work in behalf of the corporate farmers.

A copy of the alliance letter, obtained by The Washington Post, said the group "remembered" and "appreciated" Watt's help in preparing a lawsuit that forced Andrus to prepare an environmental impact study before moving ahead with the proposed regulations.

Watt was away from his office yesterday, unavailable for comment, but departmental attorney Moody Tidwell rejected the notion that Watt's involvement in ordering the delay this week was a conflict of interest. w

"First, Secretary Watt didn't take the action. Dave Russell did," Tidwell said. "Second, even if he had taken the action, it would not have fallen within the recusal commitment. This was only a delay so the department can get a handle on the issue.It wasn't a substantive issue."

The order this week affects a process that would have ended in mid-March, when time for comment on the proposed regulations would expire. The department then could either move ahead with the new rules or withdraw them for redrafting.

Watt's action was described yesterday by Rep. George Miller (D-Calif.) as "a very, very serious violation of what Mr. Watt promised the Senate and a violation of what his role is supposed to be as the trustee of public resources."

Miller, a member of the Interior Committee and a leading advocate of strict enforcement of the 1902 law, added, "It is not a minor incident, and I am very disturbed. It is a conflict, pure and simple. The phrase has been used about the fox guarding the hen house. Well, with this, the fox has just started to eat the chickens."

Miller indicated that he would work to have Watt called before the committee again to explain this week's action.