With the opening of the 1980 Maryland General Assembly session, Prince George's and Montgomery County legislators are singing a familiar song -- one which might be aptly labeled "The Metro Blues". Its chief theme: Convincing the state to pay the bill for the suburban Maryland share of the Metro subway.

"This session is zero hour for us," commented Sen. Howard A. Denis (R-16). "Our backs are to the wall and our hands are out."

Like Denis, most Montgomery and Prince George's legislators said they consider Metro funding their number one priority in Annapolis.

Pressure on the legislature to act quickly has been increased by President Carter's approval of a $1.7 billion federal aid bill for Metro. To obtain the funds, the suburban counties must come up with a "stable and reliable" source for the state and local share of Metro funding. To most delegates, "stable and reliable" means state money.

In the past, the state has paid most of the Maryland share of Metro construction costs and the 20 to 25 percent of its operating costs. After federal and state aid funds were deducted, Montgomery and Prince George's paid for the rest out of property tax revenues. Under one recent state task force proposal, the two counties would pay 25 percent of the Maryland share of the operating costs, and would be empowered to impose up to a 1 percent local sales tax for that purpose.

Winning a favorable Metro package will depend heavily on the ability of Montgomery and Prince George's members to garner support from other Maryland legislators.

Last year, the two delegations failed in part because Baltimore, with its powerful bloc of votes, helped kill legislation that would have allowed the state to fund Metro with sales tax revenue.

That move by Baltimore, which has all construction and operating costs for its mass transit system paid for by the state, set off a bitter dispute in which Montgomery and Prince George's legislators lined up in one corner and the governor and rest of the state legislature lined up in another.

In the end, the legislature found no solution for transit financing but Gov. Harry Hughes and top legislative leaders appointed a task force to come up with ways to finanace the two Washington suburban counties' mass transit costs.

Under a plan proposed by a task force subcommittee, the state would provide funds for the construction and operation of Metro and the Baltimore mass transit systems and the maintenance and some construction of the state's deteriorating highway system.

The plan may draw opposition from Baltimore. The proposal calls for the state to pay 100 percent of construction costs, and 75 percent of operating costs. At present, Baltimore gets 100 percent funding for both.

"They've been getting a free ride and they're not going to give that up easily," commented one political observer.

The task force plan calls for raising both the gasoline tax and the motor vehicle registration fees to furnish revenue for the transportation program. A penny would be added to the state's nine-cents-a-gallon tax on the price of gas. Registration fees would rise by $10. In addition, Montgomery and Prince George's counties would be authorized to impose a one percent general sales tax for transportation purposes.

However, the revenue raising proposals have had a mixed reception in the county delegations.

"If we can pay for the transit system without raising taxes, we will," said state Del. Robert S. Redding (D-23), chairman of the Prince George's 24-member house delegation. "It's kind of difficult to argue for a gasoline tax increase when the state is wrestling with what looks like a big budget surplus." The state expects a $229 million surplus for the current budget year.

Del. David L. Scull (D-18), chairman of the 22-member Montgomery house delegation, was critical of the gas tax because it did not rise with inflation. dHe also noted, "People are not receptive to tax increases when the state has a big surplus."

Sen. Victor L. Crawford (D-20), who heads the Montgomery delegation on the Senate side said, "If we are going to sell the voters a gas tax to fund Metro, we should decrease the sales tax from five cents to four cents."