PEORIA, Ill. (AP) _ Caterpillar Inc. said Friday it was at an impasse in negotiations to end the United Auto Workers' four-month-old strike against the construction equipment maker. The UAW denied that talks were stalled.

''Caterpillar has made three contract proposals to the union,'' the company said in a statement. ''The UAW has rejected each offer out of hand and offered no counterproposal or compromise.''

''Regrettably, we are clearly at an impasse,'' Caterpillar said. The company said it had notified the union Thursday of its position.

UAW Secretary-Treasurer Bill Casstevens responded in a statement, saying ''The only reason for management to proclaim its one-sided view of 'impasse' would be to further ... despicable union-busing tactics.''

''The UAW remains ready to bargain,'' he said.

Caterpillar has 16,000 UAW workers at plants in four Illinois communities and in York, Pa.; Memphis and Denver. More than 1,600 are on layoffs, and 10,800 members are on strike, all in Illinois.

When a company attempts to declare negotiations at an impasse, it could signal that management plans to begin making unilateral changes in the workplace, a spokesman for the National Labor Relations Board said.

''Normally, an employer would be declaring its intention to implement some or all of its last and final offer. That frequently results in the union filing a charge with the NLRB, saying that negotiations are not at an impasse,'' said Larry Brennan of the NLRB's office in Milwaukee.

After negotiations broke down, a limited strike was declared by the union Nov. 4 with 2,400 assembly-line workers walking off their jobs in East Peoria and Decatur.

Caterpillar retaliated Nov. 7 by locking out 5,650 union workers at factories in Aurora and East Peoria.

The locked out workers joined the strike Feb. 16 when the union rejected Caterpillar's offer to return to work.

The UAW's three-year contract with Caterpillar expired Sept. 30. Under that pact, Caterpillar's union workers earn an average $17 an hour, or about $35,000 a year.