President Reagan will reward "kitchen cabinet" member and head talent scout William A. Wilson with a post of his own, naming him special delegate to the Vatican, according to well-placed sources.

Not that Wilson needs work. The 66-year-old longtime friend and adviser of the president is a millionaire southern California investor who first suggested to Reagan that he buy a ranch in the hills north of Santa Barbara.

At the time Wilson owned a ranch there. He has since sold it but maintains a Mexican hacienda where Reagan and his wife Nancy vacation each year.

Since the election, Wilson has been a prime mover on the Presidential Personnel Advisory Committee, originally headed by William French Smith before Reagan named him attorney general. Wilson now heads the committee, which after the inauguration moved into the Executive Office Building and screened political affiliations and philosophies of prospective appointees.

Wilson, an athletic-looking cattle rancher who serves on the boards of various big businesses and is a Reagan appointee to the University of California board of regents, said his talent-scout role is nearly finished and that he hopes to return to California Sunday.

He said the committee, dominated by those who have been called Reagan's "kitchen cabinet," had tried to "search out people who have been loyal to him, who shared his philosophies and who were willing to make a scarifice to serve their government."

The job-screening has been disappointing to some conservatives, who maintain that key posts in the adminsistration have been filled by those not basically Reaganites. Wilson dismissed this criticism, in words similar to those used by Reagan at his press conference last week, saying there were many more job-seekers than jobs and that some people were therefore bound to be unhappy.

"After all, look how many votes I had," Reagan said last week, without dealing with the issue of whether conservatives were being sidetracked. "You can't reward them all."

Wilson said yesterday he is aware his name had been mentioned for various posts, including Vatican delegate and ambassador to Mexico.

"Until I've been told officially, I don't know what I'll be doing," he said when asked about the Vatican appointment.

The position pays expenses only and is traditionally given to a wealthy Catholic who can afford, as Wilson can, to serve at the Vatican and do the requred entertaining without salary.

Wilson, who has known Reagan since the president's days as a General Electric spokesman two decades ago, was converted to Catholicism 35 years ago. He is one of the few Catholics in the predominantly white, Protestant presidential inner circle.

A white House official, asked his opinion yesterday of the prospective appointment, responded by asking whether Wilson was Catholic. Assured he was, the aide said: "Good, it will ensure us of a supply of blessed rosaries."