JOLIET, Ill. (AP) _ Members of the machinists union have ended a 28-day strike at the Caterpillar Inc. plant here, accepting a new contract that provides no pay raise but offers a $580 bonus and improved benefits.

''I don't think you can say there's a winner in this type of situation,'' said Joe Misener, spokesman for the International Association of Machinists and Aerospace Workers' Local 851. ''I think it was an acceptable compromise.''

The union represents 2,400 workers at Caterpillar's Joliet components plant.

Members voted 1,659 to 426 Thursday to accept the 32-month contract, giving them a new holiday in honor of the Rev. Martin Luther King Jr., an improved pension and profit-sharing increases. It also gives them two extra days off in 1987. Members will go back to work beginning Monday evening.

Since the strike began Aug. 1 at the Joliet components plant, Peoria-based Caterpillar has laid off 1,885 workers at plants in Peoria, Decatur and Aurora because of disruptions in getting parts to manufacture its earth-moving equipment.

''The company is relieved that the 28-day strike is over,'' said Caterpillar spokesman Don Weir. ''The new contract is beneficial to all concerned - employees, union and company. While providing improved employee benefits, it also allows the Joliet plant to continue its efforts to modernize its facilities and cut costs.''

The new contract reduces the number of job classifications and broadens job descriptions, and it calls for putting about $1 million aside to compensate workers whose jobs are downgraded.

Caterpillar will recall the workers on temporary layoff at its manufacturing plants as soon as the Joliet plant produces enough components to put them back to work, said company spokesman Brian Gareau.