A couple of months ago, Robert Jantzen did what hundreds of other good American citizens have done since Election Day 1980 -- he quit his job, packed up his worldly goods and emigrated to Washington to take up government service under the new administration.

But it appears that the shimmering future he saw through the desert haze of Phoenix may well have been a mirage.

Jantzen, formerly the director of the Arizona Game and Fish Department, had been offered the post of head of the U.S. Fish and Wildlife Service. As is standard for expected-designees who haven't been formally nominated, he took up duties as a special assistant to his prospective boss, Interior Secretary James G. Watt, and started learning the ropes.

Now it appears somebody else will get the job he came to Washington to fill. In a recent letter to Sen. Barry Goldwater (R-Ariz.), White House counselor Edwin Meese III said somebody else was under consideration for the job Jantzen expected to get.

That "Somebody" reportedly is Norman C. Roberts, a San Diego investment counselor, financial analyst and former veterinarian. Those may not sound like sterling qualifiactions for the job, but Roberts' resume shows a little plus -- he was a county chairman for President Reagan's 1976 and 1980 campaigns.

The statutory provisions for the Fish and Wildlife Service post say that the director must be "by reason of scientific education and experience, knowledgeable in the principles of Fisheries and wildlife management." It's possible that the White House may be able to pour a little snake oil on that requirement -- Roberts once pursued a doctorate in herpetology.

Jantzen's supporters -- who included Rep. Eldon Rudd and Sen. Barry Goldwater, both Arizona Republicans -- are a bit mystified by the turn of events. "I just can't believe it," said Rudd. "It's crazy."

Jantzen, pursuing Interior Department business in Denver with Ray Arnett, who as assistant secretary for fish, wildlife and parks would have been his immediate superior, couldn't be reached for comment.

But another Interior staff member said Jantzen is aware of the situation, adding somewhat mournfully: "He just bought a house here in Springfield."