President Carter warned the House yesterday that the defeat of legislation to implement the Panama Canal treaties would not nullify the treaties but would have a "very serious consequence" for American interests in the Canal Zone.

At an interview with out-of-town editors at the White House, Carter said the narrow margin by which the legislation passed a test vote in the House Thursday was "very disappointing and very disturbing to me."

The House, where some members are still simmering over being exluded from any role in approving the canal treaties last year, Thursday approved a rule spelling out procedures for the debate on the implementing legislation by an unexpectedly close 200-to-198 vote.

The narrowness of the margin caused House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) and other supporters of the bill to postpone a scheduled vote on the measure next week.

It also provoked a White House counterattack yesterday in the form of warnings from the president and his press secretary, Jody Powell, that defeat of the implementing legislation would not achieve the objective of members of Congress who opposed the treaties.

"They [the treaties] are the law of the land," Carter told the editors. "They became effective the first day of April. The Panama Canal Zone will become Panama's territory on the first day of October 1979, no matter what the Congress does this year on implementation."

The treaties, approved by the Senate last year, will gradually turn over control of he canal and surrounding Canal Zone to panama. Among other things, the implementing legislation would provide funds and authorization for the U.S.-Panamanian commission that will run the canal between now and the end of the century, for the initial turnover of U.S. canal zone property to Panama and for the payment to Panama of profits from canal tools.

Rejection of the implementing legilation, the president said yesterday, would confront the country with "a very serious consequence."

"We could not handle the problems or needs or obligations for and to American workers there," he said."We could not transfer workers from one place to another. We couldn't deal effectively with the Panamanian workers who have been employed there for many years."The citizenship status and basic rights of Americans in the Panama Canal Zone would be in doubt. We could not provide for the facilities and equipment to defend the canal. In the fact, the operation of the canal itself might very well be interrupted," he said.

The chief argument of opponents of the legislation is that the administration has concealed and deliberately underestimated the cost of transferring the canal to Panama. Some opponents, including in their calculations estimates of the value of the land to be transferred, have said the land is worth from $10 billion to $14 billion and that additional transfer costs could run as high as $4 billion.

Powell yesterday said the total costs to the United States will be about $800 million, not $4 billion. The administration does not include land values in its cost calculations.

Powell also reiterated Carter's warnings on the possible defeat of the implementing legislation. Accusing the bill's opponents of adopting a "cut-off-your-nose-to-spite-your-face attitude," Powell said:

"if the House defeats the legislation, it will not invalidate the treaties. It will not mean the Panama Canal will not be transferred to Panama."

He said some House members, acting with "a substantial lack of information," seem to feel that would be the effect, when in fact defeat of the legislation would accomplish nothing "except to harm the United States, and particularly our employes in the Canal Zone."