The chief executive of an industrial supply company in Brooklyn pleaded guilty on Wednesday to selling counterfeit spare parts for subway cars and buses to the Metropolitan Transportation Authority, prosecutors said.

The businessman, Joseph Ungar, 47, of Brooklyn, was accused of passing off less expensive knockoffs as the products of standard ball-bearing manufacturers.

Prosecutors said he also created an elaborate web of deception to support his activities, even assuming the identity of a dead businessman on the telephone and in writing.

“The counterfeit parts were inferior in quality and workmanship to the material that should have been supplied,” Robert M. Morgenthau, the Manhattan district attorney, said at a news conference.

Mr. Ungar’s company, Abec Industries, distributes bearings, gears and other power transmission products. It pleaded guilty to separate charges on Wednesday.

Barry L. Kluger, the inspector general of the authority, said in a statement, “When a dishonest vendor sells counterfeit parts, the M.T.A. loses both the protection of a reputable warranty and the quality assurance of genuine equipment.”

Authority officials said, however, that although some of the parts made their way into vehicles, the public was never in danger.

Mr. Ungar pleaded guilty in State Supreme Court in Manhattan to charges including grand larceny, tax evasion and scheming to defraud. Abec Industries pleaded guilty to trademark counterfeiting and identity theft.

Avraham C. Moskowitz, Mr. Ungar’s lawyer, declined to comment when reached by telephone on Wednesday.

According to court papers, between 2003 and 2008, the authority awarded three procurement contracts to Abec Industries: two for the ball bearings used in subway car motors and one for the bearing assemblies used in bus transmissions.

Mr. Ungar claimed that the parts were made by well-known manufacturers, but in reality they were knockoffs made in China, prosecutors said.

“In the aggregate, we’re talking about thousands of parts,” Jordan Arnold, the assistant district attorney who worked on the case, said at a news conference.

In 2004, the authority declared Abec a nonresponsible bidder after the company failed to submit accurate information. However, Mr. Ungar was able to continue to supply spare parts by using different personal and professional names, prosecutors said.

Abec Industries adopted various identities, including Omega Engineering and Bearing Inc. and Rockwood Pulley Manufacturing Company, while Mr. Ungar himself claimed to be a number of different people in his communications with the authority, according to court papers.

One of his alter egos, the papers said, was Irving Patron, the founder of a bearing distributor, now defunct. Mr. Patron died in 2005.

Mr. Ungar’s activities were uncovered by a joint investigation by the offices of the authority’s inspector general and the Manhattan district attorney.

Mr. Kluger said workers suspected that something was amiss in 2006 when “an alert employee noticed something suspicious about the packaging and the serial numbers.”

Although some of the counterfeit parts were already in use when the fraud was discovered, metallurgical testing revealed that they were not substantially weaker than the proper bearings. While they would not last as long, there was little risk of a catastrophic failure that could endanger riders, a spokesman for Mr. Kluger’s office said.

Therefore, the parts that had been used were replaced in the course of routine maintenance.

Alongside the fraud investigation, investigators also discovered that Mr. Ungar had evaded taxes on the vast majority of his personal income from 2003 to 2007, and had also avoided paying New York City taxes on Abec’s corporate income.

Prosecutors said Mr. Ungar agreed to a sentence of five years’ probation and a lifetime ban on doing business with the authority. He must also pay more than $330,000 in restitution, criminal fines, taxes, interest and penalties.

Abec has agreed to pay $5,000 in criminal fines and go out of business, Mr. Morgenthau’s office said.

Mr. Kluger said Mr. Ungar’s punishment sent a strong warning to others who might consider selling counterfeit goods to the authority.

“Simply put, the message is: You will be punished, pay us back, and never do business with us again,” he said.

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