The Federal Communications Commission announced yesterday it has "strongly admonished" the American Broadcasting Company for its "negligence and careless conduct" of the U.S. Boxing Championships Tournament.

The network suspended the tournament April 13, 1977, at the end of six telecasts after investigating such allegations of irregularities as inaccurate records of boxers as provided by The Ring magazine.

The FCC said it has requested ABC to advise the commission within 30 days of steps it has taken or will take to prevent a recurrence.

Roone Arledge, head of ABC news and sports, could not be reached by telephone at his office for comment.

The commission concluded that ABC was negligent in not having acted sooner to investigate fully rumors allegations, information and incidents regarding the integrity of boxers' rankings by the magazine and the alleged involvement of Don King Productions in kickbacks or booking fees.

King organized the tournament and ABC agreed to fund it in the amount of $2,035,000.

The FCC statement said numerous incidents occurred prior to the first telecast in January 1977, which should have alerted the network to investigate earlier than it did. Two investigations later were undertaken by the network.

The commission pointed out that ABC's attempts to maintain integrity by such means as obtaining affidavits did not offset its failure to investigate thoroughly tournament irregularities repeatedly brought to its attention by its staff as well as from outside sources.

The commission said that while the tournament was represented to the public as being open to qualified boxers based on Ring's rankings, the last three telecasts did not mention that some ranked fighters were not participating.

In that connection, the FCC said that during an interview after the second telecast, ABC broadcast a statement by the promoter, King, that other fighters with high ratings to the opportunity to enter the tournament before the semifinals; that on Feb. 14, 1977, the president of ABC essentially repeated the promoter's offer during a newspaper interview and stated that fighters who believed they were excluded could contact the network; yet on Feb. 24 the chairman of the tournament rules committee said no one else could enter because that would breach contracts with fighters already participating.

The commission said that apparently no announcement of that decision was made to the public.

In a separate statement, Commissioner Tyrone Brown said that although he wholeheartedly concurred in the FCC's decision to admonish the network he noted that the so-called Armstrong Report submitted after one of ABC's investigations indicated a good deal of unethical behavior by individuals involved with the administration and organization of the tournament.

Brown pointed out that Don King Productions and The Ring magazine were identified as the major entities responsible in those areas.

"The commission," Brown said, "could be viewed as casting dispersions (sic) on the principals of Don King Productions or Ring magazine without providing those individuals with an opportunity to respond . . ."

"Under the circumstances, I wish to emphasize that the commission's letter of admonition is not intended to reflect on any individual or organization other than ABC. It is intended solely to hold ABC responsible for its failure in this case to conduct its affairs in the manner expected of a broadcast licensee."