The United States formally asked its NATO allies today to speed up their long-term defense modernization programs to help compensate for the spreading of the American military umbrella over the Persian Gulf.

European officials were said by American sources to respond positively to the broad measures outlined by U.S. officials, which now will be studied by NATO members.

The favorable initial European response contrasted with the cool reserve shown by allied governments to most other U.S. initiatives since Soviet troops invaded Afghanistan in late December. In this case, however, as one official noted, the United States simply is seeking an acceleration of programs already generally agreed to by the allies in a long-range modernization program drafted two years ago.

The U.S. request was delivered by Under Secretary of Defense Robert Komer to a meeting of senior defense officials from NATO's 15 member countries.

In a background briefing afterward, a senior U.S. Defense Department official said Komer explained to the Europeans the changed "facts of life" about American military strategy since the Soviet invasion.

Komer is said to have assured the Europeans that the United States is not currently contemplating any reduction of U.S. forces now in Europe. But he reportedly made clear that the possibility that U.S. forces could be diverted to the Persian Gulf now means that the Europeans must carry more of the burden for defending their own continent.

Recent U.S. calls for European support in defending the gulf region were not discussed at today's meeting, according to the official, who stressed that Komer simply explained what the United States alone might have to do. There was also no discussion of the possibility of a U.S. naval blockade against Iran, the official said.

The meeting reportedly focused only on NATO plans to strengthen forces in Europe. In this regard, NATO defense ministers are expected at their semiannual meeting next month to approve the acceleration of a wide assortment of improvements ranging from a buildup in munitions reserves to a general upgrading of troops' combat readiness.

In addition, the United States called on Europe to:

Increase the readiness of its reserves, many of which are not assigned to units or not equipped for rapid deployment.

Enlarge storage areas for war equipment.

Develop plans, as the United States has done, to commander civilian aircraft if necessary for the rapid airlifting of U.S. troops to Europe.