The battle over the law governing the Central Intelligence Agency's covert operations broke out yesterday in the House Foreign Affairs Committee with a conflict on the crucial issue of when Congress should be told of them.

A Foreign Affairs subcommittee last week approved a proposal that would require advance notice, but Rep. Clement J. Zablocki (D-Wis.), the committee chairman, countered yesterday afternoon with an amendment that would allow the president to ignore the rule whenever he thought it necessary.

Both plans would sharply reduce the number of congressional committees that would share the secrets.

The current law, enacted in 1974 as an amendment to the Foreign Assistance Act, calls for reports to all the "appropriate committees" of Congress, a description that now covers seven House and Senate panels. The new legislation would restrict such notices to the House and Senate Intelligence committees.

The 1974 law, known as the Hughes-Ryan amendment, is somewhat ambiguous on when the reports are to be made. Conflicting interpretations, although written down years ago, have surfaced in the past week.

A study by the Congressional Research Service, conducted in 1975 but just made public by Rep. Les Aspin (D-Wis.) concluded that advance notice is already required under Hughes-Ryan.

The Justice Department then made public a portion of a secret opinion drawn up in 1977 for then-Attorney General Griffin B. Bell, which drew exactly the opposite conclusion. Lawyers for the Justice Department's Office of Legal Counsel held that it was "clear from the legislative history [of Hughes-Ryan] that reports to Congress need not occur before the operation is conducted."

A Justice Department spokesman said the rest of the 10-page opinion on the Huges-Ryan amendent was being kept secret for "strategic reasons." He denied that the portion dealing with the prior-notice issue was being released with an eye on the congressional debate. He said it was made public this week at Bell's request simply by coincidence, as the result of a newspaper interview with the former attorney general.

In practice, the CIA generally notifies the House and Senate Intelligence committees, and several other panels such as Foreign Affairs, in advance of its covert operations. But President Carter has come out strongly against writing the practice into law, contending that this would encroach on his constitutional prerogatives.

The dispute has already led to an impasse between the White House and the Senate Intelligence Committee over a legislative charter for the CIA. tThe charter would also repeal Hughes-Ryan, but progress on the charter legislation has been slow.

In the House Foreign Affairs Committee, Rep. Lee H. Hamilton (D-Ind.) sponsored the subcommittee version that would require notification to Congress of covert operations "prior to the initiation of such operation."

Zablocki moved yesterday to tack on a proviso that would permit the president to wait whenever he decides that prior notice would "prejudice" the operation itself, the national security, or the lives of the individuals involved in the operation. An aide to Hamilton indicated he feels exceptions should be made only when lives might be endangered. The issue may come to a vote today during the full committee's markup of this year's foreign aid bill.