WASHINGTON — A U.S. district judge Monday blocked the federal government from funding all research involving human embryonic stem cells on the grounds that it violates a 1996 law intended to prevent the destruction of human embryos.

The ruling came in the form of a preliminary injunction in a case involving two scientists who challenged the Obama administration’s stem cell funding policy, which was designed to expand federal support for the controversial research.

The Obama rules allowed the use of stem cell lines derived from frozen embryos no longer needed for fertility treatments that were donated according to strict ethical guidelines. The rules did not allow the National Institutes of Health to pay for the creation of the stem cells themselves — a process involving the dismantling of days-old human embryos that is clearly forbidden by a federal law known as the Dickey-Wicker Amendment.

The scientists who challenged the guidelines argued that Dickey-Wicker also forbids the use of federal funds for any subsequent research on those stem cells, even if the embryos they came from had been destroyed years before.

U.S. District JudgeRoyce C. Lamberthagreed in a 15-page ruling.

It was “”the unambiguous intent of Congress to prohibit the expenditure of federal funds on ‘research in which a human embryo or embryos are destroyed,’ “” Lamberth wrote, citing language from Dickey-Wicker.

The Department of Health and Human Services, which operates the NIH, had argued that the act of creating embryonic stem cells was distinct from research that used the cells to study the development of genetic diseases or to create replacement cells that might treat conditions such as diabetes, Alzheimer’s and the paralysis that results from spinal cord injuries.

But research is a long, continuous process that can’t be partitioned into discrete pieces, Lamberth wrote. If Congress meant to prohibit funding only to specific scientific acts, it could have said so. “”Congress, however, has not written the statute that way, and this Court is bound to apply the law as it is written,”” the ruling says.

The NIH and the White House declined to comment on the ruling Monday and referred calls to the Department of Justice.

“”We’re reviewing the judge’s ruling,”” department spokeswomanTracy Schmalersaid Monday evening.

Lamberth issued the injunction because the plaintiffs —James L. Sherleyof the Boston Biomedical Research Institute andTheresa Deisherof AVM Biotechnology in Seattle — have “”a strong likelihood”” of winning their case at trial. In the meantime, he said the researchers and “”the public interest”” would suffer irreparable harm if federal tax dollars were used to study human embryonic stem cells.

“”The Obama administration has attempted to skirt the law by arguing that they are only funding research after the embryos are destroyed,”” saidCharmaine Yoest, chief executive of Americans United for Life, an anti-abortion public policy group. “”That administration policy is in violation of the law.””

But embryonic stem cell researchers said the decision throws the field into turmoil.

“”The long-term practical impact is a massive halt to most embryonic stem cell research in the U.S.,”” said Dr.Irving Weissman, director of the Stanford Institute for Stem Cell Biology and Regenerative Medicine.

Scientists working with embryonic stem cells said patients will also suffer by having to wait longer for science to develop new treatments and cures.

Advanced Cell Technology Inc. is using the cells to grow retinal pigment epithelium cells that restored vision in rats and mice with a rare childhood disease called Stargardt’s macular dystrophy. The Santa Monica, Calif.-based company has asked the Food and Drug Administration for permission to use the cells in a clinical trial. But without any prospect of federal funding, the research would be in doubt, said Dr.Robert Lanza, the company’s chief scientific officer.

“”This is criminal,”” Lanza said. “”We are talking about people going blind, people who dying from a terrifying array of diseases.””

Even in California, where Proposition 71 made billions of dollars available for research involving human embryonic stem cells, scientists face a chaotic future because so many rely on NIH grants, saidAlan Trounson, president of the California Institute of Regenerative Medicine.

During the Bush administration, when federal research funds could be used on only a handful of human embryonic stem cell lines, many scientists operated parallel labs supported entirely with state and private funds. It was an inefficient and expensive work-around that scientists were eager to abandon after Obama’s election. But Monday’s ruling would force them to return to that practice.

“”It’s going to be chaos,”” Trounson said. Researchers will have to furlough some of their staff in order to keep their labs open, he predicted.

It is unclear whether the ruling would force current NIH grants for human embryonic stem cell research to come to a halt, or merely prevent the agency from doling out new money for the work. Lamberth said his injunction “”would simply preserve the status quo and would not interfere with (scientists’) ability to obtain private funding for their research.””

But the NIH has invested $395 million on human embryonic stem cell research since 2005 and is projected to spend another $127 million this year. Under Obama, the NIH has deemed at least 75 human embryonic stem cell lines eligible for use in federally funded projects, including five that were approved for use under Bush.

University of California-Los Angeles law professorRussell Korobkin, an expert on stem cell legal issues, said the ruling was “”a terrible decision.””

By considering all research part of an unbreakable continuum, the decision implies that the Dickey-Wicker Amendment has no limits, which is an “”unconvincing”” interpretation, Korobkin said. “”It suggests that by conducting research on an acorn a scientist would also be conducting research on an oak tree, because acorns come from oak trees.””

The NIH has maintained since 1999 that the Dickey-Wicker Amendment precludes only the derivation of human embryonic stem cells, not their use as an experimental tool. The fact that Congress has not fine-tuned the law since then to explicitly ban funding for the research is evidence that the NIH is correct, Korobkin said.

The case originally included the Christian Medical Association, an embryo adoption agency called Nightlight Christian Adoptions and other plaintiffs, but courts removed them from the case.

An appeals court allowed the two researchers to proceed on the grounds that the expansion of NIH funding for human embryonic stem cells made it more difficult for them to win grants for their work on other types of stem cells derived from adult tissues.