The United States warned today that NATO could become "a relic of the past" unless Europeans carry out pledges to improve their military capability and link their new intervention force firmly to the Western alliance.

"There will be no EU caucus in NATO," Defense Secretary William S. Cohen warned in an unusually passionate speech to NATO defense ministers, part of it from handwritten notes. The United States will demand unity in the alliance, he said.

In his final appearance at the annual meeting, and with the identity of the next U.S. president still undecided, Cohen said any attempt to create a rival to NATO might weaken or even destroy the 19-nation Atlantic alliance.

He told reporters that he had warned fellow ministers that the allies, as a priority, must carry out their promises to improve NATO's defense capabilities. Without that, "NATO could become a relic of the past," Cohen said.

U.S. and other officials said the speech was greeted by a moment of stunned silence, then loud applause. It seemed certain to propel the question of European Union security policy back to the forefront of an already overladen agenda at the EU summit in Nice this week.

NATO Secretary General George Robertson said Cohen "was right to warn us, and ministers were right to listen" to his message that "if they get a lot of things wrong, then NATO will be irrelevant." He stressed that "we all believe the transatlantic alliance remains fundamental to our security and NATO" is its cornerstone.

At the center of the controversy is the European Union's plan to form a rapid reaction force of 60,000 troops by 2003 for use in peacekeeping and other crisis situations in which NATO does not take part. There has been no agreement so far from the EU on a U.S. demand that any operations undertaken by the new force be coordinated and planned under the mantle of NATO.

Some allies see France, an EU member and the only NATO ally that does not belong to the integrated military structure, pursuing its own political agenda and sowing the seeds of a rival alliance in the fledging Rapid Reaction Force.

French Defense Minister Alain Richard said he did not view Cohen's words as a warning, nor did he feel they canceled out Cohen's far more positive remarks about an autonomous European defense project at a ministers' meeting in Birmingham, England, in October.

But Richard said that "we certainly have a different view" that all military planning must be done through NATO.

The 51-year-old alliance faces a choice "between vitality and decadence," Cohen said.

The United States, he said, needed to know that all allies were as committed as it was to NATO, and he said too many questions about the EU plan were still unanswered.

He said alliance nations in Europe must commit more to improving their military capabilities as agreed, and that a "cooperative, collaborative mechanism" must be established so that the EU force was not a competitor with NATO.

"If there is openness, transparency and a noncompetitive relationship, then the United States would remain committed," Cohen said.

But "if, in fact, we had lip service being paid to developing the capabilities, if we had a competing institution that was established that would be inconsistent with military effectiveness, if in fact there was any element of using the [EU] force structure in a way to simply set up a competing headquarters . . . then NATO could become a relic," he said.