Despite a last-minute appeal from two Agency for International Development officials who put their jobs on the line over the issue, the Regan administration remains firmly opposed to an international advisory code on infant formula, a White House spokesman said yesterday.

Deputy press secretary Larry Speakes said the United States will vote against the proposed code Thursday at a World Health Assembly meeting in Geneva because the administration "did not want to vote to outlaw something abroad that we would not do so here at home. We did not want to establish the World Health Organization as an international Federal Trade Commission."

AID officials Eugene N. Babb and Dr. Stephen C. Joseph condemned the administration's decision at a news conference yesterday. Both denied reports that they had been pressured to resign, but confirmed that they would do so if the United States casts what may be the 156-member assembly's only vote against the code.

"I find this position unconscionable," Joseph, the agency's highest ranking health professional, said yesterday. He cited "numerous studies" showing that artificial infand deeding "is associated with higher rates of illness and dealth" in developing countries.

In announcing the U. S. position last Friday, the State Department said there was no convincing evidence of a link between the use of the formula and infant mortality in Third World countries.

The administration also has said that the code, if adopted in the United States, would violate First Amendment rights and antitrust laws. Its supporters do not dispute that, but they note that the code is recommendatory -- to be put into effect in accordance with the laws of each country -- and that a "yes" vote from the United States would not force adoption of the code in this country.