WASHINGTON (AP) _ President Clinton says Caterpillar Inc. and striking workers should settle their bitter dispute ''in a spirit of cooperation'' and that the company should not threaten to hire permanent replacements.

''I believe that the threat or implementation of replacing striking workers has a poisonous affect on relationships between workers and employers and that it does great damage to the collective bargaining process,'' Clinton wrote Donald Fites, Caterpillar's chairman, in a letter released Thursday.

The Peoria, Ill.-based company immediately began advertising for and started hiring permanent new employees after the June 20 strike, stressing they were not replacements for the strikers.

Caterpillar's director of labor relations has said there was a chance the new hires could become replacement workers. But he said that would depend on factors such as attrition rates, demand for machinery, legal obligations to rehire the strikers and the status of complaints filed by the National Labor Relations Board.

The United Auto Workers union struck plants in Illinois, York, Pa., and Denver, affecting 13,300 employees at the world's largest maker of earth- moving equipment.

Joe Velasquez, deputy director of political affairs at the White House, said Clinton was asking both the company and the union to ''return to the table and start negotiating and work out the problem.''

Caterpillar viewed the letter, dated Tuesday, as Clinton's last-minute effort to sway Senate votes on legislation to outlaw the permanent replacement of striking workers. The bill was effectively killed for the year on Wednesday.

''We respect his position, but we had a different position on that issue, as everyone knows,'' said Keith Butterfield, a Caterpillar spokesman.

Caterpillar remains in close contact with federal mediators and believes their involvement is ''an appropriate and productive approach to restarting negotiations,'' he said.

Alan Reuther, the UAW's legislative director, said the union was ''very grateful'' for Clinton's position that ''it's wrong for employers, including Caterpillar, to use permanent replacements.''

''Obviously the president carries a lot of moral authority,'' he said.

In the letter, Clinton reminded Fites that he walked the picket line during an earlier strike as a presidential candidate in 1992,

''I want to challenge companies like yours that have been split by this issue to move forward to new chapters of cooperation and economic revitalization and I hope that spirit can be shown by both sides as you work through your current dispute,'' Clinton said.

Clinton said he did not want to take sides in the dispute, but that he wanted to ''express my hope that both sides can together work out these differences in a spirit of cooperation which allows you to get back to the business of creating jobs and quality products.''

Whatever the bill's outcome, Clinton, wrote, ''I strongly believe that this practice must stop because it deters the type of collective bargaining and cooperative work forces that we need to prospect in the new world economy.''