Accused by its conservative adversaries of laxity, fumbling and inconsistency ever since gaining power 10 months ago, France's Socialist government this week showed it could get tough, laying down the law on issues as diverse as police discipline and budget deficits.

Interior Minister Gaston Defferre removed two of France's top police officials, who sought to defy his authority. And President Francois Mitterrand for the first time made it clear that the government would have to postpone or cut back social reforms that had been promised or already enacted because it is running out of money to finance them.

Dogged by continuing recession, rising foreign trade deficits and a threatened franc, Mitterrand seemed to be preparing public opinion for possible abandonment of his policy of trying to spend France's way out of its doldrums.

Defferre effectively broke the career of Marcel Leclerc, the head of the prestigious Paris crime squad. Betraying Parisian contempt for the provinces, Leclerc turned down a promotion involving a transfer to Marseilles, Deferre's home town and a center of crime.

Technically, Leclerc was on sound ground since a Paris police privilege entitles the capital's officers to turn down provincial postings. As a result, Leclerc was shunted aside to an inspection job--what Paris police call "the broom closet."

His boss, Francois Le Mouel, who made his reputation in the late 1960s by busting the "French connection" heroin smuggling ring, backed Leclerc and got fired.

Defferre named his own men to the top Paris jobs, trumpeted the importance of provincial posts in the new decentralized France he is charged with overseeing and disregarded a lukewarm demonstration by about 400 of the fired men's friends at police headquarters.

Conservative politicians and opposition newspapers accused Defferre of giving in to two pro-Socialist police unions that were said to have been gunning for Leclerc for years. He stood accused in those quarters of favoritism in such unsolved political murders as those involving Prince Jean de Broglie, a onetime conservative minister; a leftwing convict-turned-writer named Pierre Goldmann, and Henri Curiel, an Egyptian-born activist on behalf of Third World causes accused by the opposition of being a Soviet spymaster.

Raymond Marcellin, who served as interior minister for six years in the wake of the 1968 student and worker upheaval, said, "A government that is no longer master of its police is no longer master of anything." He was commenting on what he felt was excessive union influence in the police--where the Socialist unions claim they control the loyalty of 70 percent of the police officers. Defferre nonetheless was credited by his supporters and others with enhancing the government's public image.

Mitterrand came closer than ever before to ordering what the French have come to call a "pause" in the train of reforms enacted since he became president in May.

Last fall he rejected such pleas from Finance Minister Jacques Delors and Budget Minister Laurent Fabius. But this week, faced with an economy more sluggish than he had expected, Mitterrand ordered strict discipline in public spending. He told the Cabinet that the ceiling for the budget deficit would be 3 percent of gross domestic product--an estimated $20.6 billion.

Mitterrand said jobs remain "the only priority," an indirect admission that next year's budget may contain few of the costly reforms promised during the 1981 campaign.

Many observers are convinced that the budget deficit this year will far surpass the original target of just under $16 billion and may be more than double that in 1983--not including $6.6 billion for burgeoning social security deficits and unemployment benefits. Contributing to the deficits were such outlays as the controversial nationalization of banking and some key industrial groups, aid to farmers, civil service pay increases, subsidies for the public sector and the above-market price paid for Algerian natural gas.

Conservatives who predicted economic and financial disaster from the moment of Mitterrand's election now are prophesying higher taxes, a further franc devaluation and inflationary printing of money. They expressed doubts that the government could keep the deficit within announced levels.

Further gloom was supplied by former prime minister Jacques Chirac, the conservative mayor of Paris, who played on recurring rumors of Mitterrand's alleged poor health--apparently belied by the president's active schedule. Chirac enigmatically said that "the opposition risks being called back more rapidly than one thinks" to running the country. Mitterrand's seven year terms expires in 1988.