The Prince George's County Council, which once planned to cut the property tax rate by a dime, voted instead last night to raise it by 4 cents because a citizen group apparently has blocked a telephone tax the Council was counting on to raise $6.8 million.

The new rate is $3.41 per $100 of assessed valuation.

The county got new taxing authority from the Maryland legislature last winter and planned to use it to impose a 10 per cent tax on phone bills. The revenue from that tax would have permitted the property tax cut.

A group called Prince George's Citizens Against Nuisance Taxes (CANT) announced Wednesday they have collected 14,000 signatures in their drive to block the phone tax. That number - if it survives a possible challenge - is enough to force the county's new "omnibus" taxing authority to referendum in November, 1978 and prevent imposition of the phone tax pending that vote.

The tax and CANT's opposition to it seem likely to be issues next year when every elective office in the county is at stake.

County Executive Winfield M. Kelly Jr., who fought to obtain the new taxing authority and the phone tax, declared at last night's Council meeting:

"I will challenge those who brought the petition drive to tell their story to the public as I will tell mine." He said he plans to "use television, newspapers and anything at my disposal" before the referendum.

Although the county raised its property tax rate by four cents per $100, the Maryland-National Capital Park and Planning Commission lowered the county's park and planning tax rate by five cents to 69 cents per $100. As a result, the overall tax rate for county property owners will be $4.10 per $100 of assessed valuation, a one cent decrease from the last fiscal year. Nevertheless, tax bills will rise because assessments have risen an average of 10 per cent in the last year.

Kelly and other proponents of the phone tax saw it as a reform that would bring badly needed tax relief to homeowners.

Kelly aide John Lally said last night that homeowners pay 80 to 85 per cent of the property taxes. He said that if the phone tax had gone into effect, apartment dwellers and commercial and industrial phone customers would have paid phone taxes totalling 4.9 million while homeowners would have paid only $1.9 million.

He said the average tax paid by each residential phone customer would have been only about $1.25 a month.

CANT argues that the phone tax would be an unfair burden on low and middle-income residents. CANT leader Tim Maloney rejected compromises offered earlier this week by Kelly and the Council, saying: "The (taxing) authority is too powerful for just the county officials to decide on alone."

Last night's vote to raise the property tax rate was unanimous. The mood was perhaps reflected by Councilman David G. Hartlove when he said: "I feel worse than being at a funeral."