After months of planning and printing, the government is finally ready today to begin circulating a redesigned, harder-to-counterfeit $20 bill.

Some lucky customers of a bank in California will get free samples right away, but most Americans will have to wait for weeks before they see the notes spitting from automated teller machines.The Federal Reserve's 12 regional banks today will begin shipping two billion new notes - $40 billion - to the nation's banks, savings institutions and credit unions.

But the old notes will always remain legal tender, Treasury Department officials stressed. And the Federal Reserve will continue circulating old notes until they wear out, on average in two years.

After six months, officials expect one in every four $20s in circulation will be of the new design, which incorporates a range of features designed to frustrate counterfeiters armed with personal computers, scanners, ink-jet printers and color copiers.

Federal Reserve officials plan more than two dozen events around the country, including one in Sacramento, Calif., with Washington Mutual. The bank will give away as much as $10,000 in new $20s in an event dubbed "WaMoola Madness."

Up to 20 people will be invited for 20 seconds to grab for bills whirling around in a glass booth. The bank will donate a matching amount to a local housing charity.

The Treasury Department has begun an $8 million public relations campaign aimed at persuading Americans to check for the new features so they're not fooled by poor-quality knockoffs.

"It's critically important that people know what to look for and that people look," said Treasury Secretary Robert Rubin.

He plans to mark the introduction of the $20 in a ceremony in Washington today with Treasurer Mary Ellen Withrow. Both officials' signature appear on U.S. currency.

The most obvious change is the larger and off-center portrait of Andrew Jackson, the nation's seventh president, on the bill's face. The reverse features a picture of the north side of the White House (instead of the south side seen on the old notes). To help people with poor vision, the bill's denomination appears in large dark numerals on a light background.

The government issued new $100 notes, with Benjamin Franklin, in March 1996, and new $50s, with Ulysses S. Grant, in October 1997. It plans to issue new $10 bills and $5 notes simultaneously in 2000 and a more modestly redesigned $1 bill after that.

The new $100s, $50s and $20s have a watermark in the shape of a portrait, visible when the bills are held to a light. They have an embedded plastic security thread that glows under ultraviolet light - red for the $100, yellow for the $50 and green for the $20.

And the numeral in the lower right corner of each denomination's face is printed in color-shifting ink. It looks green when viewed straight on and black when viewed from an angle.