WASHINGTON (AP) _ George Bush's inauguration Jan. 20 will cost more than $20 million and feature a half-dozen free events in addition to balls and dinners at up to $1,500 a ticket, the Presidential Inaugural Committee said today.

''This inauguration is different because we're going to try to have more free events than at any inauguration before,'' said committee co-chairman Bobby Holt.

The free events range from a children's festival commemorating 200 years of inaugurations to a White House welcome for the public on Bush's first morning in residence there. The most expensive event is the Inaugural Dinner Jan. 18 at Union Station, at $1,500 per person. A ticket to one of eight official balls goes for $175, but $30 will get you into a Young American Ball.

Holt said the budget for official inaugural events sponsored by the presidential committee will be $20 million to $25 million. The money is being raised as interest-free loans that will be repaid with proceeds from ticket sales and other inaugural marketing.

Holt said loans of $100,000 or more are being accepted, but smaller in-kind contributions are also welcome. Walter Ganzi Jr., the committee's finance chairman, said about half the money needed has been raised.

Both the presidential committee and a bipartisan congressional committee in charge of the oath-taking ceremony are leaning heavily on the bicentennial theme.

Some of the trappings of Bush's inauguration ceremony would look familiar to George Washington: 13-star flags, for example, and red bunting and the First Great Seal, which was the newborn nation's emblem from 1782 to 1841.

But metal detectors and 140,000-plus spectators surely would have startled the first president.

Bush's bicentennial inauguration ceremony combines the old and the new, with the most dramatic change the introduction of security precautions for the first time.

The West Front of the Capitol, the site of the Jan. 20 oath-taking, will be accessible only through four gates equipped with metal detectors. All guests will be screened before the ceremony - a prospect that strikes terror in the heart of a key organizer.

''My worst nightmare is that 50,000 people will show up at 11:20 a.m. for a ceremony that starts at 11:30,'' said Michael Ruehling, executive director of the Joint Congressional Committee on Inaugural Ceremonies.

Hoping to attract early arrivals, the congressional committee will open the gates at 9 a.m. and has scheduled a musical interlude by the U.S. Marine Band at 10:30 a.m. ''The only thing we're not providing is popcorn,'' Ruehling said. ''I don't know what else we can do, but it does scare me.''

The Constitution stipulates that the oath of office must be taken at noon, so latecomers will be out of luck.

Bush will be sworn in against a backdrop of five flags - two from 1789, with stars representing the 13 original states; two from 1889, with 38 stars, and one flag with the current 50 stars.

He'll step onto the platform through an archway festooned with red bunting similar to the bunting draped over the door of Federal Hall in New York when Washington was sworn in for his first term in 1789. The plan is for Bush to take the oath on the same 1767 Bible that Washington used. And all inaugural materials will bear the First Great Seal.

As has become custom, Bush's inauguration ceremony will be more elaborate than the first one 200 years ago. At Federal Hall, Washington simply bowed to his audience, repeated the 35-word oath of office and added, ''I swear, so help me God.''

This year, music will be provided by the U.S. Marine and Army bands and the Harlan (Ky.) Boys Choir. The Rev. Billy Graham will deliver the invocation and the benediction. Chief Justice William Rehnquist will administer the oath of office to Bush, while Justice Sandra Day O'Connor will swear in the vice president, the congressional committee said.

Inaugural planners are working ''to make it a little extra special'' in light of the bicentennial, Ruehling said.

The expanded program is designed as a souvenir, with four pages of inaugural history in addition to the schedule of events. In addition, for the first time, the program will name the president and vice president instead of referring to them by their offices, as has always been the case previously.

The Bush inauguration marks only the second time the ceremony has been held on the Capitol's West Front. From his podium, Bush will have a panoramic view of the grassy Mall, the soaring Washington Monument and many grand buildings of the city.

President Reagan was sworn in there in 1981. But most inaugurations have taken place on the East Front, which overlooks the asphalt Capitol parking area as well as the landscaped Capitol grounds.

The inauguration platform and stands under construction on the West Front are costing $323,000 to build. Taxpayers are paying for the inaugural preparations and also for an hour-long lunch for 200 in the Capitol's Statuary Hall.