NEW YORK (AP) _ The National Dairy Board has been illegally promoting an experimental growth hormone for dairy cows, a critic of the hormone says in in a lawsuit.

Jeremy Rifkin, president of the Washington, D.C.-based Foundation on Economic Trends, said he filed the lawsuit Thursday after discovering that the dairy board had contracted with a public relations firm to promote the growth hormone.

Rifkin has used various legal maneuvers to try to block the use of bovine growth hormone on the grounds that it is unsafe for humans.

The latest action is based on documents he obtained under the Freedom of Information Act that Rifkin says show the dairy board was working in collusion with the growth hormone's makers to promote it.

He also petitioned the U.S. Food and Drug Administration on Thursday to ''immediately halt any promotion of this product by FDA officials and to immediately rescind the use of this product in the marketplace until it is approved.''

The FDA is considering whether to approve the hormone for routine use, but it has already allowed milk from experimentally treated cows to be released for human consumption.

Yvonne Dock, the dairy board's spokeswoman, said she had no comment on Rifkin's action or his remarks. William Grigg, an FDA spokesman, also had no comment, saying the agency had not yet seen the petition.

Grigg defended the decision to allow consumption of milk containing the hormone.

''The safety to human beings is clear,'' Grigg said. He said the hormone has no effect in humans and occurs naturally in milk, ''so we've always consumed it.''

Rifkin and other critics have charged that the hormone could have deleterious effects on human health. Questions have also been raised about the economic consequences of boosting the milk supply and thus presumably lowering milk prices.

Rifkin said the dairy board is prevented by law from promoting such substances before they are approved by the FDA.

''The dairy board cannot put out any information regarding efficacy or safety of a product before its approval,'' Rifkin said. ''It is a violation of the law. Nor can they collude and be in meetings with private companies to be in such a campaign.''

The lawsuit seeks to block the board ''from continuing with their campaign to promote this product,'' Rifkin said.

The board was set up by Congress to help increase the consumption of dairy products produced in the United States, said Maureen Bergen, the board's director of advertising and promotion programs.

The Department of Agriculture oversees and approves its expenses, she said, but the board is funded by dairy farmers, not the government.

The documents obtained in Rifkin's Freedom of Information Act request include minutes of an April meeting in which the board agreed to spend $1,085,000 on a public relations firm ''for the management of the BST issue.'' BST stands for bovine somatotropin, the technical term for the hormone.

In a March 12 letter obtained by Rifkin, Ernest Miller, chairman of the board's industry and public relations committee, said that the law requires that no board funds ''are to be spent to influence legislation on regulation.''

''If NDB (the National Dairy Board) were to become proactive on BST while it is still under government review, that action could be construed as lobbying on behalf of the pharmaceutical companies,'' the letter continued.