Northwest Airlines has agreed to pay a $325,000 fine to the Department of Transportation, which had accused the carrier of violating federal consumer protection rules.

The airline said it did not admit to violating DOT guidelines, but agreed "to settle the matter to avert costly litigation that would result if it challenged the DOT penalty."

The DOT cited three problems: Refunds on unused tickets were not paid promptly. Passengers bumped from overcrowded flights weren't always informed of their rights. The airline didn't always inform customers that some of its flights are operated by smaller regional airlines using propeller-driven aircraft instead of jets.

Northwest spokesman Red Tyler said the airline had refund problems last year and early this year that have since been corrected.

He said the government's complaints on bumping and regional airlines resulted from differing interpretations of federal rules and have been remedied by increased training.

Tyler said Northwest encountered refund delays shortly after merging with Minneapolis-based Republic Airlines in August 1986 and didn't get refund operations back on track until early in 1987.

Federal regulations require airlines to provide refunds in seven days for tickets purchased with credit cards and in 20 days for tickets purchased with cash. Northwest now meets that requirement, Tyler said.

In the case of overcrowded flights, Tyler said ticket agents did not always fully inform all passengers of their rights when they were denied boarding, and that the problem was resolved with improved training.