Amendments to cable TV copyright legislation that would effectively nullify a court decision restricting cable telecasts of sports events are expected to be approved today by the House Judiciary Committee, sources close to the committee said.

The amendments, part of a comprehensive cable copyright legislation package, would define suppliers of cable television companies as common carriers, and, as such, make them exempt from copyright liability. The legislation would continue to make widespread cable transmission of sporting events possible.

Earlier this month, U.S. District Judge Neil P. McCurn in Syracuse, N.Y., ruled that Eastern Microwave Inc. (EMI), which services a total of 1,300 cable-television companies with a total of 5 million subscribers, was in violation of federal copyright laws in transmitting New York Mets baseball games without the Mets' permission.

Since 1965, EMI has picked up signals from New York City's WOR-TV for rebroadcast to the cable companies it supplies. In addition to the Mets, WOR-TV broadcasts games of the New York Knicks, the New York Rangers, the New York Islanders, the New Jersey Nets and the Cosmos of the NASL.

In essence, the judge held that that retransmission of the WOR signals by EMI was a "public performance" and therefore subject to copyright laws. In a similar case last fall, a judge in Chicago ruled the opposite in a case involving WGN-TV and United Video Inc.

Sources close to the Judiciary Committee said it had always been the legislative intent that cable supply companies such as EMI and United Video would be exempt from copyright liability and that the purpose of the amendments is to make that intent explicit. Spokesmen for professional sports interests denied that this was ever the case.

Under current cable copyright law, cable television companies are permitted to telecast sports events without permission of the teams involved simply by paying a nominal fee into a pool, from which copyright holders are reimbursed. In 1978, the total amount of money paid into the pool was $12 million, but only a fraction of that was for sporting events.

For the last several years, the issue of cable copyrights as they involve sports has been especially delicate, with team owners contending they should have the right to exercise more control over broadcasts. Cable companies and subscribers have pressed for minimal or no restrictions.

Spokesmen for major league baseball and the National Basketball Association endorsed Judge McCurn's decision and said yesterday they deplored the Judiciary Committee's action to effectively nullify it.

"Baseball was pleased by the decision," said Chuck Adams, a spokesman for Commissioner Bowie Kuhn. "If it were to stand, it could help to restore the balance between the cable television companies and the clubs."