NEW YORK (AP) _ It will be a poor man's Liberty Weekend, without laser beams, fireworks or tall ships. Ronald Reagan is staying in Washington, Francois Mitterrand in Paris. If ticker tape flies it will be for the New York Mets, not the Statue of Liberty.

But ceremonies Monday and Tuesday for the statue's 100th birthday do have the advantage of historical precision: the statue was unveiled and dedicated by President Grover Cleveland and French officials on Oct. 28, 1886.

Three main events are planned for the two-day celebration: a Monday afternoon ceremony on Ellis Island to honor dozens of Americans of diverse ethnic backrounds; a rededication ceremony the next day, Oct. 28, on Liberty Island; and a Tuesday night concert at Lincoln Center.

The latter, ''Liberty's Centennial Gala: The All-Star Finale'' is called that because ''people keep asking, 'Is this the end?','' according to organizer Nancy Sureck.

After an extravaganza on the scale of July's Liberty Weekend, anything would seem anticlimactic, said U.S. Interior Department spokesman Alan Levitt. ''We're not trying to outdo Liberty Weekend, because it's impossible to do that,'' he said. ''We'll have a low-key celebration.''

This week's festivities actually are two celebrations, organized separately by the organizations of two men: Lee Iacocca, who as chairman of the Statue of Liberty-Ellis Island Foundation led a campaign that raised about $300 million, and Donald Hodel, who as Secretary of the Interior controls the statue and the island.

Hodel fired Iacocca earlier this year from a government advisory panel in a dispute over the use to which Ellis Island will be put.

The Ellis medals ceremony and the Lincoln Center concert are foundation affairs, while the Liberty rededication is an Interior Department production.

Hodel has been invited to the concert and Iacocca to the rededication, but neither was invited to speak at the other's event.

The Oct. 28 rededication will feature speeches by Hodel, Treasury Secretary James Baker and Arman Avedisian, the man Hodel chose to replace Iacocca.

Among the invited guests are Gov. Mario Cuomo, Mayor Edward Koch and a delegation from France. There also will be room for about 3,000 members of the public.

The Ellis Island Medal of Honor ceremony grew out of a controversy that erupted after 12 immigrants were chosen to receive the Medal of Liberty from President Reagan during Liberty Weekend. Members of some ethnic groups felt left out, and now, a larger group will be honored.

Among the medal winners expected to attend Monday are developer Donald Trump, former boxer Muhammad Ali and former baseball star Joe DiMaggio.

But less than three-quarters of the medalists said they would attend. No- shows included singer John Denver, former First Lady Jacqueline Kennedy Onassis, actors Gregory Peck and Kirk Douglas and actresses Claudette Colbert and Helen Hayes, guitarist Carlos Montoya, golfer Arnold Palmer and tennis star Martina Navratilova.

James Tamer of Mount Clemens, Mich., declined his medal after it was learned he was a convicted bank robber slated for inclusion in the Nevada Gaming Commission's ''Black Book'' of undesirables. He had been described by a ''Lebanese activist'' by the group that chose the medalists.

The ceremony will be followed Monday night by a $250-a-plate dinner at the Waldorf-Astoria hotel to raise funds for the statue and island and to honor the medalists. Entertainer Bob Hope will be honored as ''immigrant of the century.''

The two-day celebration ends Tuesday night with the musical salute, which will feature the world premiere of ''On Freedom's Ground: An American Cantata'' by William Schuman, with a text by poet Richard Wilbur. The piece will be performed by the New York Philharmonic, led by Zubin Mehta, and a 200- member chorus.

Later, Julio Eglesias, Charles Aznavour and Placido Domingo will sing.