National Grid is suing 34 Rhode Island cities and towns, accusing some of inflating the assessments on its gas lines and, as a result, overcharging the company on its tax bills.

National Grid argues in a suit filed in Providence Superior Court that a dozen communities have been assessing its gas mains, meters and other equipment at higher rates than state law permits, resulting in “arbitrary, excessive and illegal” taxation. It asks the court to order all the cities and towns to change the way they assess gas lines and to order specific communities to reimburse National Grid for excess taxes paid.

The suit does not specify how much the company believes it is owed. But company spokesman David D. Graves said the reimbursement amounts would be negotiated individually if the court rules in National Grid’s favor.

“We’re just asking for an equal and equitable application of state law,” Graves said.

The company claims in the suit filed Nov. 5 that conflicting state laws are at play. It argues that communities, including Warwick, Cranston and Newport, have been assessing gas equipment as real estate under an outdated state law.

National Grid alleges that, instead, the gas distribution lines should be declared “personal tangible property” for taxation purposes under a law passed two years ago. The value of those assets should then have been depreciated under set guidelines, the suit says.

The company argues the General Assembly intended to replace the older law when it enacted the more recent law. The cities and towns, the suit says, have not only over-assessed the company’s property, but have invoked an illegal tax by failing to apply the procedures laid out by state law.

In addition, Rhode Island law requires ambiguities in revenue statutes to be resolved in the taxpayer’s favor, the company asserts.

While the suit does not pinpoint how much it is seeking, it details the differences between particular assessments. It names the tax assessors and finance directors in each community as defendants.

Warwick showed the most striking discrepancy. There, the city valued National Grid gas equipment at $47 million in 2007, compared with the company’s calculation of $23.4 million.

In Cranston, the divide between its assessment of gas lines and the company’s ranked about $6.4 million last year. In Pawtucket, the discrepancy hovered at about $7.3 million.

Other communities identified as owing National Grid included Central Falls (with a $491,849 discrepancy), Coventry ($456,131), Cumberland ($888,279), East Providence ($36,236), Glocester ($5,584), Newport ($8,001), North Kingstown ($3), Portsmouth ($2,248) and West Warwick ($340,262).

Warwick City Solicitor Peter Ruggiero estimated the total amount the company seeks at $2 million throughout the state, approximately $400,000 of which would come from Warwick.

“The city intends to vigorously contest this,” Ruggiero said. He added there have been ongoing going questions about the conflicting laws and suggested that the General Assembly might take up the issue in the coming session.

National Grid is Rhode Island’s dominant utility company, providing electricity service to 477,000 customers in 38 communities and natural gas to about 245,000 customers in 33 communities.

kmulvane@projo.com