When Ronald Reagan was sworn in four years ago, he appointed hundreds of conservative supporters to high-ranking government jobs. Many of them moved here from the West and South, pledged to make fundamental changes in the federal bureaucracy and prepared to encounter a hostile environment in the nation's capital.

Today, as their political hero begins a second term, most of the 1,700 full-time presidential appointees are settling in for four more years, too.

Concerns some of them may have had about living in the bastion of liberalism and big government have been overshadowed by the discovery that their presence here has helped change the atmosphere -- and that maybe the atmosphere was not so bad in the first place.

With a conservative president in power, institutions and individuals who for so long were outsiders, noses pushed against the window of the establishment, are now the insiders. "There is a totally different feeling around town," said Edwin J. Feulner Jr., president of the Heritage Foundation, a conservative think tank.

Feulner noted that the current issue of Washington Dossier magazine, a sensitive barometer of capital ins and outs, lists him and Burton Yale Pines, his vice president for research, among "Washington's Mighty 500, Potentates of Power and Influence." If that had happened five years ago, Feulner said, "Everyone but my wife and kids would have laughed, and Dossier's reputation would have been damaged."

A few presidential appointees lived up to pledges to stay just a while in Washington: William Clark, who served as a State Department official, national security affairs adviser and secretary of the interior -- "never took his cowboy boots off," according to one White House observer, and Clark is headed back to California. So is Attorney General William French Smith, who lived out of a suitcase at the Jefferson Hotel. A few more, such as secretary of the interior James Watt and Environmental Protection Agency director Ann Gorsuch, were asked to leave.

But most Reaganites have succumbed to Potomac Fever, at least while Reagan is still president. Whether they will stay beyond 1988 remains to be seen, but tradition -- and the large number of officials from administrations dating to Franklin Roosevelt who settled here -- suggests that the longer one stays, the harder it is to go home again.

When Frank J. Fahrenkopf Jr. was named chairman of the Republican National Committee two years ago, he told his family in Reno, Nev., that he would be in Washington for two years. His wife, Mary, stayed in Nevada with their three daughters. At the end of the school year, however, they decided to come here to live for a year so the girls could experience living in Washington.

That year was up last August, but the family was having such a good time, they decided to stay on until Fahrenkopf's term at the RNC came to an end. But in November, Fahrenkopf decided he would accept a second term, and now Mary Fahrenkopf is looking for a house.

"Famous last words," Mary Fahrenkopf said, and she laughed, recalling their original intentions.

The easy acceptance of life in the capital by some conservatives annoys some of their hard-line brethren. "They came here to get a job, not to do a job," said one. Another offered this axiom: "When one of our people gets into power, he ceases to be one of our people." A few went home, disillusioned, said one who stayed, "when they found out this the Reagan administration is no revolution."

But a pragmatic conservative noted, "If you really think that America is the greatest place on earth, and this is the White House and I'm here, then this is where you belong."

Theodore B. Olson came here from Los Angeles in February 1981 to be assistant attorney general for legal affairs, a position that amounts to being the attorney general's lawyer. Olson had been in the same law firm -- Gibson, Dunn & Crutcher -- as the new attorney general.

"We did not discuss how long I would stay," Olson said the other day, "but I thought it would be two or three years." But Olson stayed at Justice until last November, and when it came time to leave, his old law firm "felt it would be a good idea" for him to stay here "for a few years" and head its 43-lawyer Washington office.

Despite initial concerns about uprooting two teen-agers from friends and school in California, Olson's children have quickly adapted. "The Fairfax County schools are a big plus," said Olson's wife Karen. "They are much more education-oriented than in Los Angeles, which were club-oriented."

Christine Olson, 18, who graduated from Langley High School last year and is a freshman at Mary Washington College in Fredericksburg, Va., "has made it clear she intends to stay" in the East, her mother said. Son Kenneth, 16, a sophomore at Langley, still looks forward to visiting his grandparents in Northern California but "doesn't miss living in Southern California at all." Karen Olson, a fourth-generation Californian, has become "a born-again Virginian."

The weather here was a pleasant surprise to the Olsons, who had been told to expect unbearably humid summers and terribly cold winters. "It does get cold," Karen Olson said, "but if you bundle up, winter can be fun. The air is clean."

Another misconception the Olsons had concerned federal workers.

"I had this stereotype that they were all overpaid and underworked; a bell goes off and everyone drops their pencils and goes home," said Karen Olson, who frankly was looking forward, in return for the paycut and move, to her husband finally having "a 9-to-5 job."

What she found, however, was a dedicated work force, not unlike that of Olson's law firm. "Some worked harder than Frank, and others worked as hard," she said.

Theodore Olson's decision to move to Washington, and stay, also changed the life of his secretary, Susi O'Neill, who came here with him.

"If you had asked me in the first six months, I would have gone back to L.A. in a minute," she said the other day. "Now, I'm real, real glad Ted is staying here."

At first, she found the atmosphere here "so different. Everyone was so committed to work, to the exclusion of other things. It seemed to be a cold place." But it was also "a beautiful city, and the cleanest I'd ever seen. I liked it from the beginning."

Now that she has returned to working at a private law firm, she hopes to have a little more time for herself. "At Justice, everything was a last-minute crisis," said O'Neill, who rents a condominium in Falls Church. "It would take a pretty appealing offer for her to leave."

Despite the attractions of Washington, many Reagan appointees still insist that home ultimately will beckon them.

Margaret Tutwiler, after a hectic first year on the White House staff, found she had time to enroll in cooking clases in Bethesda, take an exercise class in Georgetown and join friends at restaurants.

But last year was busier than ever. She was White House liaison to the president's campaign committee, she worked on the inauguration, and she plans to stay on in some role in the second term.

"I stay because of new challenges, to test myself," she said. "But at some point, I am definitely going back to Birmingham, Ala.