FBI Director William H. Webster announced yesterday that federal agents have cracked a major heroin ring in New York involving members of two of New York City's five organized-crime families.

The announcement came after agents of the Drug Enforcement Administration, a division of the FBI, seized 13 suspects with almost 21 pounds of heroin worth more than $20 million. Agents also seized two handguns and $23,600 in cash.

On Oct. 14 President Reagan announced plans to hire more than 1,000 federal agents to set up task forces throughout the country to attack the drug problem.

Webster said the undercover operation, which culminated Wednesday night when arrests began on a street on the east side of Manhattan, had "immobilized" an operation that was importing more than 55 pounds of heroin into the United States each week.

He said the men arrested were members and associates of two traditional organized-crime families in the New York area. Since the investigation is continuing, Webster refused to identify those families. But another official, who asked to remain anonymous, said they were the Bonnano and Luchese families.

Kevin Gallagher, head of the heroin desk at DEA, said the arrests, which followed a 16-month investigation, began around midnight Wednesday when undercover agents "flashed" $1.9 million in cash, which was to be the payment for the heroin. Officials said the meeting took place in the area of 55th Street and First Avenue on the East Side.

DEA officials said the heroin ring was not of the magnitude of the French Connection case in New York in the early 1970s, but said it was one of the largest operations in recent history.

Agents previously purchased six pounds of heroin from two of the suspects for $501,000 in an effort to give the government's undercover operation some credibility.

"We have seen for the first time here an important connection that we have been able to demonstrate between organized crime and heroin," Webster told a news conference.

He said the suspects "have a history of violence and represent some of the country's major traffickers" in heroin. John C. Lawn, deputy administrator of the DEA, added that all 13 suspects have felony backgrounds and some have been convicted of murder.

Officials said the group also dealt in cocaine and was supplying drugs to another major metropolitan area, but Webster declined to identify it.

Those arrested were identified as Oreste Anthony Abbamonte, 34, of Port Washington, N.Y.; Joseph Thomas Del Vecchio, 39, of Englewood Cliffs, N.J.; Frank (Albie) Genovese, 39, of Brooklyn; William (Crazy Willie) Irizarry, 56, of New York; Frank Irizarry, 53, of New York; Rafael Gonzalez, 35, of New York; Lorenzo Di Chirara, 48, of Brooklyn; Armand Casoria, 63, of Fort Lee, N.J.; Benjamin Mallah, 57, of New York; Gerald Salerno, 52, of Dix Hills, N.Y.; Bernice Castillo, 62, of New York; Anthony Torres, 60, of New York, and Frank Fuentes, 52, of New York.

They were charged with conspiracy to distribute heroin, which carries a maximum prison term of 15 years for a first offender and a $25,000 fine. Bail ranged from $5,000 to $3 million.

Webster said the suspects were importing heroin from the Golden Crescent area of Southwest Asia -- Iran, Pakistan and Afghanistan -- which supplies about 55 percent of the heroin smuggled into this country.

Attorney General William French Smith and DEA Administrator Francis M. Mullen Jr. recently visited Southwest Asia on a fact-finding trip involving drug trafficking and refugees.