The first group of Cabinet nominees Ronald Reagan will announce is likely to include only two of the "big four" posts, a Reagan aide said today.

The aide also indicated that Thursday is the most likely day for the first Cabinet announcements. Reagan will be in Washington then on his second visit to the capital since his electoral landslide Nov. 4 over President Carter.

As he boarded an Air Force plane in Los Angeles to fly to New York today, the president-elect said: "When we get to Washington, I hope we'll be able to announce some names. We have been delayed by the new ethics act.It's the first time it has been put in operation for a transition."

It had been expected that the first group of Cabinet nominees would include the attorney general and the secretaries of state, defense and the treasury -- the "big four." However, Reagan has encountered complications in his selection of secretaries of state and the treasury.

He reportedly wants Alexander M. Haig Jr., White House chief of staff under President Nixon and a former NATO commander, as secretary of state. But both the Republican and Democratic Senate leaders, Sen. Howard H. Baker Jr. (R-Tenn.) and Robert C. Byrd (D-W.Va.), have said it may be difficult to obtain Senate confirmation of Haig because of his controversial role in the Nixon administration. [Leaving Los Angeles today, Reagan said that questions about Haig's role in Watergate would have "no effect whatsoever" on whether he is the choice for secretary of state.]

George P. Shultz, at one time a candidate for either secretary of state or treasury in the Reagan administration, asked that his name not be considered. William Simon, the first choice of some Reagan advisers for treasury, withdrew his name from consideration, reportedly after learning that he would not be selected for the job.

William French Smith, Reagan's personal lawyer, appears to be the president-elect's choice for attorney general, and Caspar Weinberger, a former head of the Office of Management and Budget, appears headed for the Pentagon.

A Reagan aide who was on the transcontinental flight to New York today said there have been no unexpected problems in selecting a Cabinet. "It wasn't something he [Reagan] was going to be pressured into doing . . .or set himself a deadline," the aide said."He checked them out with a lot of people."

Immediately after his Nov. 4 victory, Reagan said he hoped to name his Cabinet by the last week of November or the first week of December.

The president-elect is scheduled to spend Tuesday in New York before flying to Washington Wednesday for a four-day visit. He is to meet with black supporters both here and in Washington.

In the capital he also is to meet with some Hispanic supporters, with Republican leaders and with prominent Washingtonians at two dinner parties.

Reagan will return to California Saturday after he and his wife, Nancy, tour the private quarters of the White House while the president and Mrs. Carter are away for the weekend.