Britain's coal miners entered their ninth month on strike today as a drift back to work gathered strength, encouraged by promises of Christmas bonuses. But the anniversary followed one of the bloodiest nights of the dispute.

Peter Wright, the chief constable of South Yorkshire, where support for the strike is strongest, said the violence last night and early this morning was "quite horrific." Clashes between pickets and police at a dozen coal pits and mining villages in the region resulted in 45 arrests, with 45 policemen and nine pickets injured.

The attacks appeared to represent a shift in tactics, police said, with violent incidents carried out by relatively small groups in several locations within a few hours. This kept police on the move. In contrast, past clashes involved large groups concentrated in one area.

Two police stations were attacked with gasoline bombs and four-inch metal bolts hurled through windows. Lamp posts were ripped up and pushed across roads to block police vehicles. Oil and glass was spread on roads and head-high wires stretched across them, according to Britain's Press Association.

Throughout the strike, about one-fourth of Britain's 180,000 coal miners have continued to work, primarily in pits still operating in Nottinghamshire, south of Yorkshire. They have kept working because the National Union of Mineworkers called the strike last March without a national ballot of the membership.

But last week, as the latest round of negotiations to end the walkout collapsed and as the state-run national coal board offered a $1,700 package of pre-Christmas wages and bonuses, the drift back to work accelerated.

The coal board said that today, about 1,900 strikers had come back to work -- almost as many as the 2,100 who returned throughout last week. The board now claims that nearly 56,000 miners are working, while 130,000 are still out.

Mine union chief Arthur Scargill accused the board of "cooking" the figures, saying about 40,000 miners were working. "The coal board's policy of trying to bribe miners to return to work, using as an inducement money already owed to them, is not succeeding," he said, while blaming the police for the rioting.

Although Scargill has suffered setbacks in recent weeks involving loss of support by some important trade union and Labor Party leaders and an embarrassing disclosure of contacts with Libya, coal board officials were reluctant to say the strike was crumbling.