The Thatcher government has begun a major review of Britain's long-term defense spending that may curtail future development of some costly new ships, aircraft or other equipment because of economic constraints and the escalating costs of new military technology.

Defense Secretary John Nott said today that Britain could no longer afford to develop and maintain such a wide range of military equipment, keep up with technological changes and maintain its primary defense roles in NATO. He indicated that the spending review will look for ways to save money by meeting these commitments with less, but more sophisticated equipment, particularly in Britain's 70 percent contribution to NATO's defenses in the eastern Atlantic.

Defense analysts here speculated that this could mean changes in ship, plane and weapons development for Britain's naval forces.

Citing the example of West Germany, which recently announced cancellation or delay of new tanks, fighter aircraft and other weapon development projects for the 1990s, Nott said: "Some of us are spreading our efforts too thinly. We are going to have to concentrate our efforts" on the most cost-effective weaponry.

This appears to conflict with the desire of the Reagan administration, reinforced by Defense Sectretary Caspar Weinberger in recent NATO meetings, for Britain and the other allies to avoid having to make such hard choices by greatly increasing total defense spending.

Nott said that Britain's defense spending will not be increased above the cost of inflation in the coming fiscal year because overspending had pushed this year's increase to 5 percent above inflation. The overspending was forced by defense contractors who delivered orders early.

Britain's annual increase in defense spending will still average about 2 1/2 percent above inflation, Nott said, compared to the agreed NATO target of 3 percent. Defense analysts here estimate Britain's military expenditure would have to grow by at least 7 percent above inflation each year to maintain all its current defense commitments, as well as plan for future equipment and weapons development.

Weinberger had urged Nott in Washington last month to consider raising Britain's military expenditure above the 3 percent target. Weinberger also reminded allied defense ministers at NATO meetings this month how much more the Reagan administration was spending on defense.

Nott told reporters today that he was certain that "the Reagan administration believes we are making a unique contribution to NATO." As examples, he listed Britain's ground forces in West Germany, its sea and air defense of the eastern Atlantic supply route from the United States to Europe, its defense of Britain itself and the many NATO bases here and its independent nuclear deterrent.

Contrary to recent speculation here, Nott emphasized that all these commitments would be maintained. In particular, he said, the commitment of 55,000 British troops in West Germany "is not under review, nor is it questioned." He also said a review of Thatcher's decision to replace Britain's present Polaris submarine-based nuclear missiles with an American-made Trident system costing at least $11 billion left him "more sure than ever that there is no other expenditure which comes near to Trident in enhancing the deterrent capability of the alliance and the defense of Europe."

Without abandoning any of its broad NATO commitments, Nott said in a defense white paper published today, "I shall be considering in the coming months . . . in consultation with our allies, how technological and other changes can help us fulfill the same basic roles more effectively in the future without the massive increase in real defense expenditure which the excalation of equipment costs might otherwise seem to imply."

In Britain's "present financial cirumstances," Nott argued, "we have too full an equipment program for the financial resources available for defense." As an example, he said, "we have some extremely expensive equipment that is not properly armed" because too much money is tied up in sophisticated ships, submarines, aircraft and tanks while too little is spent on the weapons and sensors they carry because of budget cuts.

Other "deep cuts in procurement of ammunition, fuel and oil, and essential spare parts" have curtailed training and British military movements "too severely," Nott added. "We must reestablish in the long-term program the right balance between the inevitable resource constraints and our necessary defense requirements."

Nott, a staunch supporter of Prime Minister Margaret Thatcher's economic strategy who was made defense minister earlier this year, said he hoped to announce the results of the spending review by late summer.

"I am doing my utmost to ensure there will not be any changes that will upset our allies," he told reporters.

He added, however, that "we may have arrived at another turning point in defense. Technological change is accelerating and the public mood has become more questioning."