There are leaders, who, after years in power, simply run out of ideas and the energy to govern. Then there is Margaret Thatcher.

Already Britain's longest-serving prime minister in this century and now well into her ninth year of power, Thatcher finds that the principal criticism currently leveled at her is that she is moving too fast, overloading the country's political system and turning off voters with the pace and scope of her programs.The complaints come as she leads some might say drags Britain through its most fundamental and sweeping package of reforms since the Labor government began erecting the welfare state in 1945.

Although her government commands a majority of 101 in the 650-seat House of Commons, Thatcher, 62, has been forced twice recently to make significant concessions to avert rebellions within her party.

Thatcher's decision to ease the impact of a wholesale reform of local government finance, for example, came only after her majority on one important parliamentary vote had slipped to an embarrassing 25.

While some observers question whether Thatcher's notoriously sharp political instincts might be starting to dull with the years, not even her most ardent critics believe that recent setbacks pose any immediate threat to her leadership.

If the divided, ineffectual political opposition did manage to mount a concerted challenge, Tory rebels would quickly rally behind her, political analysts believe.

But her government's declining popularity, indicated in recently published opinion polls and in heightened public outcry against some of the reforms, has generated the first significant political storms for Thatcher since her re-election last June.

Among the elements of Thatcher's reform package:

The first comprehensive review of the country's popular, but financially strapped, National Health Service since it was established 40 years ago. Government officials talk of broadening private health insurance coverage, then charging for selected medical services, but formal proposals are not expected until the fall.

A sweeping reform of primary and secondary school education, setting more rigorous standards, a national core curriculum and national performance examinations administered at ages 7, 11, 14 and 16. The bill is expected to clear Parliament later this year.

Radical changes in the welfare system, aimed at simplifying and redirecting benefits, but which have left many of the country's elderly and poor with less income. The changes were effective in April.

A reform of local government finance by extending taxation beyond property owners to all residents, who would be forced to pay a flat rate community charge. The unpopular idea, which translates into identical local taxes for millionaires and welfare recipients, was quickly dubbed a "poll tax" by its many opponents.

In a country that tends to tolerate rather than welcome major change, some argue the discontent stems as much from the scope of the reforms as from their content. But even Thatcher's closest aides admit that mistakes have been made.

"When you are doing all these things, intimately touching the lives of all 55 million inhabitants and not just special interests, then there is going to be unease," said a senior government source. "(But) the reality is that there are problems here. They are being rectified as best as possible."

To rescue the tax reform bill in the House of Commons, Thatcher was forced to agree to $250 million in rebates for lower-income wage earners and their families.

In her second retreat in as many weeks, Thatcher was forced to add $190 million to her social security reform package to prevent another rebellion by Tory members of Parliament, who have been deluged by mail from angry constituents destined to suffer under the plan.

The additional welfare benefits will go mainly to low-income individuals, many of them pensioners, whose savings would otherwise have disqualified them.

Under similar intense public pressure, Thatcher earlier this year provided an emergency cash injection into the National Health Service. Then, last week, she approved a 15 percent wage increase to the country's nurses after they had staged token strikes to protest low pay and under-funded health services.

"There is the worry that her determination may outrun her good sense," commented Essex University political scientist Anthony King.

Those close to her, however, say that her readiness to give ground on such issues merely underscores the fact that she remains responsive.