After centuries of obsessive secrecy and medieval rituals, Freemasons have turned to the modern arts of public relations and advertising for an unprecedented recruitment campaign in America.

The days when newcomers could join only by a whispered invitation from an existing “brother,” followed by a lengthy initiation, are coming to an end after a steady fall in membership.

The Grand Lodge in New Jersey has launched its most energetic recruitment drive so far, investing about $100,000 in newspaper and cinema advertising to publicize a one-day entry “class” in March. Robert Leonard, a New York public relations executive handling the campaign, needed no introduction: He is a Mason.

“If you’re looking to make a difference, take a look at Freemasonry,” read the advertisements in 12 New Jersey papers. “We are committed to charity, brotherhood, friendship, and faith and do so through philanthropic and humanitarian acts. Become a better man, father, husband, and citizen at the Freemason’s one-day class on March 19.”

Daniel Wilson, the state’s grand master, makes no apology for the new tactics. “Freemasonry has long been thought of as a secret society,” he said. “We thought it was time to educate people about what Freemasonry is all about.

“There has been a steady decline in membership numbers, and it is time to turn that around. I believe there are plenty of men looking for the camaraderie and fraternalism that we provide.”

The Web site features a greeting from Mr. Wilson in full regalia, a fact sheet on Freemasonry, and a list of prominent Masons ranging from President Washington (one of 14 presidents) to Harry Houdini and John Wayne.

Membership in America peaked at 4.1 million in 1959, largely the result of a surge in new members who had fought in World War II. But now it is only about 1.7 million, many of them getting on a bit. There are no official links between American Freemasonry and the British organization.

The main thrust of the campaign is the one-day entry class. Previously, it could take months to complete the three Masonic “degrees” required to become a member, a complicated process that lodges believed was deterring applicants.

Conspiracy theorists accuse Freemasons of secretly plotting to take over the world’s governments, while some religious groups label them a dangerous cult.

Such perceptions exasperate members who point out that their charitable work raises more than $750 million a year.

Grand Master Richard Fletcher, head of the national Masonic Services Association, hopes to capitalize on interest in Freemasonry resulting from “National Treasure,” a new film starring Nicolas Cage and Sean Bean. The plot features a fabled treasure safeguarded for the nation by the Freemasons, whom it depicts as honorable and trustworthy.

In New Jersey, home to 32,000 Ma sons, several hundred people have already signed up for the March session. Other states have also used the one-day classes to good effect, even without newspaper advertising: In Ohio and Pennsylvania, they brought in several thousand new members.

The New York State lodge, which has run the commercials, had a harder time after an unofficial initiation ritual went horribly wrong.

In March, Albert Eid, a veteran Freemason, thought the gun he was firing at a new recruit held blanks but instead accidentally shot him dead with a live bullet.

Although Masonic leaders said guns were banned from lodges, the incident was unwelcome publicity.

Freemasonry, which has its roots in the guilds of stonemasons who built the castles and cathedrals of the Middle Ages, has historically shied away from public exposure and relied on a code of signs and rituals at meetings held behind closed doors.

The new approach has annoyed some traditionalists, but Grand Masters Wilson and Fletcher said the colorful customs and traditions would not be abandoned. The special handshakes, the recitations, and the rolled-up left trouser leg are here to stay.

Nor are women about to be admitted to the male-only inner sanctum, although in America they are allowed to join affiliated organizations.

“We’re not changing things willy-nilly,” said Mr. Fletcher, 70, a retired banker and a Mason for 48 years.

“We’re not going to stand on street corners and try to lasso every passing male. But we do want to attract new members. And we believe there is a generation out there who want to get involved with a value-based organization again.”