The White House, pleading a crowded schedule, declined yesterday to arrange a meeting between President Reagan and more than a dozen House members who want to urge him to reconsider the administration's decision to vote against the proposed worldwide ethical code for marketing infant formula and other breast-feeding substitutes.

The code may be acted on today by the World Health Assembly in Geneva, Switzerland.

Rep. Tom Harkin (D-Iowa) said he told White House congressional liaison aide William J. Gribbin that he could not believe that Reagan could not spare 10 minutes to discuss an issue "that potentially involves the lives of up to a million babies a year and that can potentially be very damaging to our foreign relations."

"It's so dumb to do what we're doing," Harkin said in a telephone interview.

Harkin, one of the signers of a letter requesting the meeting, is co-sponsor of a pending bipartisan House resolution to endorse the code. The resolution bears 82 signatures.

Although the State Department said last week that the United States would be the only one of more than 150 nations to vote against the code, which sets nonbinding advisory guidelines, code supporters circulated unconfirmed reports yesterday that U.S. diplomats have persuaded Argentina, Chile, El Salvador and Guatemala to instruct their delegations in Geneva to join the U.S. opposition.

The department has asserted that there is no convincing evidence of a link between use of the formula and infant mortality in the Third World.

At least in tone, this contrasts with an April 9 memo from Dr. John H. Bryant, the Department of Health and Human Services' deputy assistant secretary for international health, to members of the Interagency Task Force on Marketing of Breastmilk Substitutes.

A relationship between promotion of substitutes and lessened breast-feeding and consequent malnutrition is indicated by a review of studies done in Brazil, Canada and Papua New Guinea, Bryant wrote in the memo, which code supporters made public.

Bryant said the Brazil study "associates" very high rates of bottle feeding and infant malnutrition with factors including "advertising of milk products through the mass media, and the role of professionals, presumably influenced by industry, who discourage women from breast-feeding."

The Canadian study, he said, showed that among mothers randomly selected on leaving hospitals after childbirth, those given samples of formula breast-fed for shorter periods than those not given the product.

In Papua New Guinea, advertising of substitutes was banned, and availability of feeding bottles was restricted, Bryant said. This "resulted in marked increases in breast-feeding and improvements in infant health [and] help to answer the question, would the code work?"

The administration also contends that it would be hypocritical to support a code that could not be enforced in the United States because it could violate federal antitrust laws and First Amendment protection of commercial speech.

The administration position will come under further attack today at a news conference to be held by backers of the House resolution and at a "forum" provided by Senate Dmocrats for code supporters.