Pressure is mounting on the Bush administration to launch a trade battle with Europe over genetically altered crops, with farm groups and their congressional allies declaring that the nation has compelling moral and economic reasons to do so.

At the same time, some in Washington are urging caution, warning that the nation could strain relations with allies over a peripheral issue when it needs every friend it can get as it prepares for war with Iraq.

The Bush administration's public statements suggest that it is moving toward suing Europe in the World Trade Organization, setting off what could be a lengthy battle. While virtually no one believes Europe can be induced to accept additional gene-altered crops any time soon, many people in Washington have concluded that making an example of the Europeans in a trade suit would help stop the spread of anti-biotechnology sentiment to other countries.

Trade sources said administration lawyers are working on the case, but are not likely to file a lawsuit until they get clearance from President Bush and his Cabinet. Two trade experts following the issue closely said a group of Cabinet secretaries is scheduled to take up the issue as soon as Monday. But it has been three weeks since Robert B. Zoellick, the nation's top trade ambassador, declared his desire to sue, and farm advocates, growing impatient, are peppering the administration with letters demanding immediate action.

"The European Union's moratorium on agricultural biotechnology has been in place for over four years with no end in sight," said a letter to President Bush this week that was signed by House Speaker J. Dennis Hastert (R-Ill.) and nine other congressmen.

Charles E. Grassley (R-Iowa), chairman of the Senate Finance Committee and an advocate for farm interests, told the publication Inside U.S. Trade this week that the administration should "get off of its duff and make a decision."

At the same time, warnings to move slowly, if at all, have come from surprising quarters in recent days -- including some of the administration's ideological allies in its effort to open world markets.

Clyde Prestowitz, once a trade expert in the Reagan administration and now president of the Economic Strategy Institute, a Washington group that advocates trade liberalization, has warned that a suit over biotech crops could backfire by inflaming European public opinion and causing domestic political difficulties for U.S. allies.

"It will be a disaster. It's just going to feed anti-American sentiment in Europe," Prestowitz said. The rest of the world would see the suit as "another case of American bullying," he said.

Starting in the mid-1990s, U.S. farmers planted millions of acres of corn and soybeans genetically engineered to resist weeds and insects. Domestic consumers have raised few objections and the crops are used to make many food products. But resistance in Europe has been intense, with opponents dubbing the plants "Frankenfoods" and major grocery chains refusing to sell them.

To create biotech crops, one or two genes are added to the tens of thousands of genes in a plant, giving the plant the ability to make, for example, a protein that fights off worms. Such proteins are readily broken down in human digestion. U.S. regulators, including the Food and Drug Administration, have concluded that biotech food is safe to eat, though some environmental questions linger.

A few biotech crops are approved for sale in Europe, but when a political controversy over the issue erupted in the late 1990s, most countries imposed moratoriums on approving more. They did not pretend to base the decision on scientific assessments. Recently, many scientific groups in Europe, including the French National Academy of Medicine, have said the food is safe.

Visiting Washington the other day, the French minister of agriculture, Herve Gaymard, said the European public was traumatized in the 1990s by public-health scandals, including mad-cow disease. which scientists believe caused cases of a rare human disease when it was spread through British beef. Scientists told the public there was little to worry about, only to be proven wrong. Gaymard counseled patience as the European public slowly regains its confidence in science.

"You can imagine how much the Europeans have been shocked," Gaymard said, adding that public opinion is nonetheless beginning to move on the issue of gene-altered crops. "Wait a little bit until there is more acceptability of these products, and then the question will be naturally settled."

The administration view is that the United States has waited more than a little bit already, and the time for tougher action is at hand. "In my position, I've waited two years to try to see if we could work with them quietly and make improvements," Zoellick said three weeks ago. "I don't see things getting improved."

Many legal experts say the administration, if it decides to sue in the World Trade Organization, would have a compelling case. To prevent countries from using safety concerns as a pretext for protecting domestic markets from foreign competition, the world's trade rules require that bans or restrictions imposed in the name of public health be based on scientific evidence. The World Trade Organization, in Geneva, would not be able to compel Europe to accept the crops even if the United States won, but it could authorize retaliation against European imports into this country.

Some experts in Washington fear a trade suit could backfire, however. "The more you try to force them, the more you're going to provoke a fight," said Julia Moore, a researcher at the Woodrow Wilson International Center for Scholars who supports the technology but not the tactic of suing.

Some experts see geopolitical implications. . The biotech-foods debate comes as the Bush administration is trying to win European support for war against Iraq.

Bush's national security adviser, Condoleeza Rice, "is probably not over there thinking about soybeans in connection with Iraq, but she should be," Prestowitz said, calling for a "a lot more quiet discussion" with the Europeans. "We have allies in Europe. We don't give them much to work with."

A tipping point in American sentiment came recently, when several African countries balked at accepting gene-altered American grain meant to feed starving people, saying they feared the grain would contaminate their domestic seed supply and hurt future exports to Europe.

A recent letter to the White House from the National Corn Growers Association and the U.S. Grains Council said, "This is not only an agricultural issue, but also one that fundamentally challenges the humanitarian ideals of developed nations to help starving people around the globe."