London — If, as expected, the British government goes ahead and creates a new fleet of nuclear- powered submarines equipped with Trident 1 missiles, it may have to make significant cuts in its contribution to NATO's conventional defense.
Prime Minister Margaret Thatcher's determination to acquire a Trident nuclear deterrent for the 1990s and beyond is unquestioned; but the economic implications of the option have been pointed out to her by an authoritative study compiled by one of Britain's leading defense experts.
Prof. David Greenwood, a specialist in defense economics at Aberdeen University, calculates that the cost of the Trident system could be as much as $ :6,500 million ($14 billion) over the next 15 years.
Unless a further increase in the overall British defense budget is authorized , he believes, such an outlay could only be met by making savage cuts in Britain's contribution to the defense of the eastern Atlantic, or by reducing the British commitment of troops and air units in West Germany.
In a special paper entitled "The Polaris Successor System: At What Cost," Professor Greenwood declares: "The price of a Trident program . . . is abandonment of the notion that Britain should make a balanced contribution to NATO."
The professor's findings have sparked additional debate about Britain's future as a nuclear power. The letters page of The Times of London has been pelted with contributions from distinguished strategists.
Some say Mrs. Thatcher should go ahead, others that she should think again. A third group questions the government's assumption that a new Trident fleet would be genuinely independent.
One of the most persuasive critics of present government planning on the nuclear question is Field Marshal Lord Carver, a former chief of defense staff. He told a parliamentary committee examining defense costs that he could foresee no circumstances in which Britain would use its nuclear force independently.
He said, "The contribution of such a weapon system is of secondary importance and would not itself justify the expenditure involved in the provision of the new system."
Lord Carver is perhaps the most authoritative spokesman among those who fear that in buttressing a British deterrent, Mrs. Thatcher might do grave harm to the nation's conventional contribution to NATO. What NATO really needs, according to this argument, is more tanks, aircraft, and highly equipped ground troops.
Professor Greenwood's intervention in the debate comes as defense planners are making budget projections for the next 15 years. Privately, some government defense specialists admit the professor has touched on a worrying issue, especially in view of Britain's general economic plight.
There is argument, too, about the planned stationing of US cruise missiles in England to counter the Soviet buildup of SS-20 missiles in Central Europe.
Two areas in East Anglia, where most of the missiles would be located, held special referendums to discover the true state of local feeling. Both votes were in favor of letting the missiles be stationed in the area.
In Parliament, however, the defense secretary, Mr. Francis Pym, has come under fire from Labour members claiming that Britain would be dealing herself into a more dangerous nuclear game by letting cruise be established on her soil.
Mr. Pym replied that if the Russians halted deployment of the SS-20, there might be second thoughts about cruise missiles in Britain but there was no sign of Moscow modifying its own medium-range missile strategy.