The Reagan administration told Congress yesterday it intends to tighten nuclear export controls by creating a new list of 63 countries that will need specific U.S. government approval to obtain any American technology for their atomic power programs.

While administration officials declined to make the full list available until the proposed new policy is completed later this week, sources said it includes such countries as Argentina, Brazil, South Africa, Israel, Pakistan, India, Iran, Iraq, Libya, Algeria and Syria. But Rep. Jonathan B. Bingham (D-N.Y.), while noting that the administration will now be taking a closer look at some deals that were routinely approved previously, said the administration did not appear to be changing the criteria under which it has approved the sale of controversial nuclear equipment.

"The criteria for making these decisions would not be changed," Deputy Energy Secretary W. Kenneth Davis agreed.

"Then these revisions do not meet some of our keenest concerns," Bingham said.

Davis and other administration officials announced the new measures at a hearing of two House Foreign Affairs subcommittees considering legislation that would tighten up the 1978 Nuclear Nonproliferation Act.

Several nonproliferation experts expressed surprise that the lengthy new list does not include a number of states that long have been viewed with concern such as South Korea and Taiwan. Administration sources said the rationale for leaving these countries off the list is that they are parties to the treaty and accept full safeguards on their atomic facilities.

On the other hand, Iran, Iraq, Libya and Syria -- which also are parties to the treaty -- are included on the list, sources said, because of their general instability at the present. All of the Communist bloc countries remain on the new list.

At hearings earlier this year, congressmen had expressed concern about the possibility that a Spanish licensee of Westinghouse Electric Co. might be able to sell an atomic power plant to Pakistan.

"Under present regulations, the Spanish company would be free to export a reactor to Pakistan," Deputy Assistant Secretary of State James B. Devine said yesterday. "Under the revised regulations, the company would be required to come to the Department of Energy for specific authorization."

Davis also said the administration had no intention of altering its present policy of refusing to make public the nuclear exports it has authorized on the grounds that to do so would harm the competitive position of American companies.

Davis and the other witnesses who testified yesterday were adamantly against proposed efforts to amend the Nuclear Nonproliferation Act to tighten nuclear export regulations.

Davis said enactment of this legislation "would have a harmful effect on our ability to engage in peaceful nuclear cooperation and trade with other countries," and would "turn other countries away from the U.S. and toward alternative cooperating partners, or increased nuclear autonomy, to the detriment of our nonproliferation objectives."