A 26-year-old New Hampshire man was arrested early yesterday on charges of attempting to extort $2 million from wealthy Washington shipping agent Harry J. Smith, the FBI announced yesterday.

Charles B. Dwyer, who was armed with a loaded.22 caliber pistol at the time of his arrest, was taken into custody at a Rye, N.H., apartment without offering resistance.

Smith's attorney, Seymour Glanzer, said that Smith received anonymous calls warning that adverse information on his shipping operations would be published in The Washington Post if he did not pay the money into a Monaco bank account.

Nick F. Stames, special agent in charge of the FBI's Washington field office, said Dwyer demanded "that Smith transfer $2 million into a bank account in Monaco on the threat of exposing alleged bribes made by Smith to foreign officials in conjunction with his international shipping business."

Smith went to the FBI in late January, after receiving extortion demands by telephone, according to Glanzer.

The Washington Post was not told of the alleged extortion attempt prior to publication of a Feb. 12 story concerning Smith. After publication the FBI informed The Post of the alleged extortion scheme.

Glanzer said The Post was "unwittingly used." Glanzer said reports of Smith's business dealings were "exaggerated and distorted." He said the transactions reported by The Post violated no U.S. laws.

On Feb. 12 The Post published a story stating that Smith's firm directed unauthorized payment of more than $150,000 in grain sale commissions to a Belgian firm which had no apparent role in the transaction.

The story reported that Smith also arranged for Jamaican purchases to be shipped by a company with which he was affiliated. Previously it was reported that two Jamaican import officials were fired for allegedly violating the country's currency laws by keeping secret bank accounts outside Jamaica.

Documents obtained by The Post revealed that the two Jamaican officials and a Liberian corporation formed by one of them received more than $32,000 from a company associated with Smith. That firm was identified as Agrobulk Shipping Corp., the company designated by Smith to ship grain to Jamaica.

Agrobulk earned itself a $900,000 profit in 1975, according to these documents, by hiring another company actually to ship the grain in a deal negotiated by Smith's firm with one of two dismissed Jamaican officials, State Trading Corp. director Dexter Rose. The other official is Sedley K. Pyne, director of the Washington office of Jamaica Nutritional Holdings, the state-owned grain-buying corporation. Glanzer says the $900,000 profit figure is exaggerated.

Subsequent documents received by The Post did identify Smith and linked his businesses to the Jamaican payments. Smith was unavailable for comment on the allegations despite repeated calls to his office, his home and his attorney.

Smith's attorney, Glanzer, now contends that his client is unable to comment until the extortion issue is resolved.

William Shaheen, U.S. attorney for Massachusetts, said the phone calls to Smith were made from the Rye, N.H., apartment of Dwyer's brother, Joseph.

Dwyer was arrested about midnight Friday by eight FBI agents at his brother's apartment. Sources familiar with the case believe that at least one other person may be involved with Dwyer in the alleged extortion scheme.

Dwyer is a 1974 graduate of Georgetown University, where he majored in English. He traveled abroad, according to relatives, living in Monaco and in Geneva where he was employed in the Australian embassy for four years.

Smith is currently president of the Georgetown University Alumni Association and has taught international shipping in the School of Foreign Service.