Peter McCoy's "great job" as the nation's first undersecretary of commerce for travel and tourism is beginning to have all the allure of a one-way ticket to South Succotash.

"I thought I would be coming over here to make a meaningful contribution to the government," McCoy said last week. "I don't think I'm doing that."

Faced with a dwindling budget, a shrinking staff and the occasionally cavalier attitude of the administration toward his little Commerce Department preserve, McCoy now says wistfully, "One of these days I'd like to be in California."

McCoy left his Beverly Hills home and the presidency of the Sotheby Parke Bernet auction house to run the White House's East Wing as Nancy Reagan's staff director. He left, he has said, for a job with "more substance," a job where he could leave his mark.

The undersecretary's job at the U.S. Travel and Tourism Administration looked like just the ticket.

And so it was that McCoy, a gentle man who picked up the nickname "Mother McCoy" on the campaign trail and was called "The Purser" at the White House because he was always nearby to hold the First Lady's purse, was sworn in as an undersecretary last Dec. 23.

The first thing he had to do was fire 40 percent of his staff. The situation went downhill from there.

The agency's Washington staff now stands at 25, with 45 more in six overseas offices. The budget, once as high as $14 million, was pegged at $5 million in the fiscal 1983 request -- "The Pentagon spills more in coffee than that," says McCoy. In fiscal 1984, even that $5 million was sliced out of the Office of Management and Budget's proposal for Commerce.

McCoy's visions of designing "a meaningful promotion program," including sales pitches to travel wholesalers and an expanded list of literature partly financed by advertising, are on indefinite hold these days while the budget goes around and around and around. And he says, almost in wonder, "There's a better recognition of the importance of travel on the Hill than in the administration."

McCoy, who learned his way around the social circles of Washington with the natural ease of a man accustomed to dealing with the rich and the powerful, acknowledges that he has a lot to learn about the city outside the iron gates at 1600 Pennsylvania Ave.

For one thing, McCoy didn't check into the financial future of the travel administration before taking the job.

"I must say I was terribly naive," he said. "Having never been outside the White House, I didn't ask. I'm not sure who I would have asked."

He also didn't have much experience in the tourism business, but after a year in the job he can spout industry figures like a pro.

"The United States gets $18 back for every $1 it spends on overseas travel promotion. It's one of the few areas where you get something back for what you spend," he says, and, "The travel industry directly employs 4 1/2 million people, and indirectly 2 1/2 million more."

He cites a few advances during his tenure. The agency has a marketing plan, if it ever gets any money to carry it out. The new interagency National Policy Council has solved a few mini-crises in the travel world, and the U.S. Customs Service has made "great strides" toward easing the way of foreign travelers in and out of the country.

And yes, he'd stay with the administration if it won another term. "I have a great devotion to Ronald and Nancy Reagan. I would do damn near anything they asked me to," he said. "But not here, not at a funding level less than what's been proposed."

And he says he won't go to the Oval Office to get that changed: "I couldn't burden the Reagans with my troubles."