If federal officials had hoped to find that local political support for the Metro subway had eroded when they ordered a restudy of the planned 100-mile system 17 months ago, they will probably be disappointed, elected area officials agree.

Many Metro boosters had suspected that the reappraisal was ordered because Department of Transportation officials wanted to study to death the planned subway extensions. But as the study progressed, many local officials found that area residents have fallen in love with Metro.

As a result, most of these local officials are unwilling to vote to eliminate any portion of the planned system. After a study that has cost more than $1 million, and after construction delays - inforced by the study - that are expected to cost tens of millions more in inflation, local governments are re-inventing the wheel.

Insteas of recommending cuts in the 100-mile system, they are on the verge recommending completion of essentially the same subway system that has been on the maps for almost a decade.

Evidence of this came last week when:

The Prince George's County Council voted to seek approval for two Metro lines in the southern county area. It had been expected to choose one of the two proposed routes, "our motto now is 103 miles or bust," said councilman Gerad T. McDonough, who offered the motion. The second line would add three miles to the system. The council had voted earlier to complete the Greenebelt line.

The Alexandria City Council, which had previously recommended that the minimum possible Metro system be constructed, reversed itself and voted unanimously to support the planned line from downtown Alexandria to Franconia, near Springfield Mall in Fairfax County.

The Fairfax County Board of Supervisors decided that the line from Rosslyn through central Arlington should terminate in Vienna at Interstate Rte. 66 instead of being rerouted to Tysons Corner. However, the board kept the Tysons Corner alternative alive by suggesting that land be purchased for a future station there.

Those decisions were reached for a number of reasons, including private polls for several area politicians that showed heavy support for Metro. Other factors involved were well-organized citizen campaigns in western Alexandria and southern Prince George's County, old-fashioned lobbying in Prince George's, and achievement of a political understanding between Fairfax County and Alexandria.

That is not the end of the story, for the hard part is yet to come. The Metro Board this spring and summer will attempt to devise a financial plan that will provide money to construct the subway beyond the 60 miles that are already funded, and then will guarantee its operating costs.

The politicians already know that there is not enough money to complete the full 100-mile system, including any modifications that come from this study, if a federal funding ceiling of about $5 billion remains unchanged.

Present estimates show that $5 billion is at least $600 million too little, and probably $1 billion too little when several essential changes are made (expansion of the already over-crowded Pentagon station, for example).

Even with that substantial hurdle ahead, however, the regional restudy has reconstructed Metro's once eroding political support, in the view of every politician interviewed.

"This study has answered literally hundreds of questions and has sifted through many alternatives to completing Metro," said Francis B. Francois, a Prince George's County Council member and the chairman of the regional study group. "People who did not live here in 1968 (when the Metro map was drawn and when referendums were passed in several counties to pay for it) now know some of the reasons," Francois said.

Perhaps the best evidence of a shift in attitudes about Metro is provided by John F. Herrity, chairman of the Fairfax County Board, a Republican running for Congress in the southern half of the county and one time a loud critic of completing the original Metro system.

"If I had known the way this (study) was going to come out," Herrity said, "I wouldn't have supported it. It was a waste of time."

Herrity said that polls taken in the county by the Republican National Committee and by Virginia Gov. John N. Dalton in his recent campaign show strong support for Metro. Even Herrity's own mail-in news letter poll, which went only to people "who called the office," as Herrity said, showed a 50-50 split on Metro. But, he added, "I don't put any stock on that. It's not scientific.

"I've shifted my thrust to another area," Herrity said. He will propose, he said, that "Fairfax County gets its own bus system," apart from Metro-bus, then use its buses to fed the subway. There's no reason for regional ownership of the bus system," he said.

The two most fascinating indications of the support for Metro were the two line decisions by the Prince George's County Council and the unanimous Alexandria City Council vote for the Franconia line.

In Prince George's County, the council previously had decided that the southern county leg of Metro should terminate just inside the Capital Beltway at Branch Avenue. It forwarded that decision to the regional committee.

After that decision, County Executive Windfield Kelly attended a meeting of the Tantallon Citizens Association, which represents a well-to-do section of the county hard by the eastern Bank of the Potomac River south of the Beltway.

There, between 200 and 300 people told Kelly in clear language that Branch Avenue was too far way for them and that they wanted the line to end at Rosecroft Raceway, about three miles closer to the Potomac and outside the Beltway.

Kelly asked the council to reconsider Rosecroft. The council did. Hearings were held. The citizens for Rosecroft were well organized, but so were those for Branch Avenue.

Rosecroft Raceway officials obviously would like to have Metro to bring crowds to the track. Rosecroft's legal counsel is the law firm that includes Peter F. O'Malley, who is extremely influential in county Democratic circles.

McDonough, the county councilman who proposed both lines, said he was called on by Ellis Koch, former county attorney and a member of O'Malley's law firm. Koch engaged in "standard lobbying" for Rosecroft, McDonough said.

McDonough also ran into O'Malley at the Capital Centre "a day or two after we had voted on Branch Avenue the first time, and Pete expressed his surprise at that decision," McDonough said. O'Malley was on vacation last week and could not be reached for comment.

But the most "intense pressure," McDonough said, came from citizens "from both sides. We decided we were going to have only one shot at getting Metro for Prince George's County; so we should go for all of it."

McDonough proposed and the council accepted, by a 6-to-5 vote, a junction in the Metro line near Wheeler Road and Southern Avenue at the District-Prince George's County line. One Metro line would go from the junction to Suitland and Branch Avenue as originally planned.The other line would go straight south from the junction to Rosecroft. The viability of such a double, "Y" line has never been studied.

Kelly said "for me, it's not an either-or situation. That was one of my lines, I like the idea ." If the council must choose one route or the other, Kelly said, he would be neutral. But he is not neutral on Metro. His polls, he said, show "fairly positve support" for Metro throughout the county.

The Alexandria City Council had voted earlier for the skimpiest of Metro systems. That would be no line through western Alexandria continuing to Franconia, near Springfield Mall.

Then some strange things began to happen. The condominium owners in western Alexandria discovered that, if organized, they have political influence. About 3,000 of them petitioned the City Council, asking that the line be continued to the Van Don Street station.

That set the stage for a deal. Fairfax County Supervisor Joseph Alexandria saw the opening and took advantage of it. It works this way:

If Van Dorn were opened it would draw many riders from nearby Fairfax County. Alexandria was under political pressure to open Van Dorn but was concerned it would get many Fairfax commuters but no Fairfax County help on subsidizing the operating costs. If the line were extended a few short miles to Franconia with Alexandria's blessing, Fairfax County obviously would be more willing to share Van Dorn operating costs.

Fairfax Supervisor Alexander personally contacted four members of Alexandria's City council and said that, in return for the city's support for the Franconia station in Fairfax County, the county would agree to share operating costs for the entire line.

Regardless of who talks to whom in both the Virginia and Maryland suburbs, the point is that significant citizen pressure has been built behind a full Metro system.

Francois, who voted against the two-route decision in prince George's County, jocularly explained it this way: "We like the line so much, we decided to have twins."