Area residents are telling their congressmen by a 2-to-1 margin that they like President Carter's energy program, except for the talk about taxes, and they are offering ideas on ways to make it better. Some of them misunderstanding it.

Suggestions abound in an unscientific survey of more than 2,100 cards and letters sent to 9 of the 10 area senators and members of congress in the past few months. The suggestions range from the advice of a seventh-grader in Warrenton, Va., about the needs of tall people to lengthy dissertations by physicists of the scientific merits of Carter's plan.

The only member of Congress who did not receive much mail on the subject was Del. Walter E. Fauntroy (D-D.C.). His assistant, Eldridge Spearman, said Fauntroy has received only eight letters about energy in recent weeks.

"I think it means substantial agreement with what he (Carter) said," Spearman theorized. "If there'd been any strong outrage or opposition, there would have been much more mail."

The rest of the area's congressional delegation, except for Sen. Harry F. Byrd Jr., (I-Va.), reported widespread acceptance of the idea that a serious energy problem exists. A spokesman for Sen. Byrd's office said no one there has has time to analyze the mail.

"People seem willing to sacrifice if they feel that will be effective and that others will make a similar effort," reported Jean McDonald of the office of Rep. Joseph L. Fisher (D-Va.). Northern Virginians, she said, "believe there's a crises we have to face . . . but they're not in agreement altogether on which set of proposals will do it."

Of more than 300 letters to Sen. William L. Scott (R-Va.), 40 discussed the President's proposed sliding tax on gasoline consumption and 36 of those opposed it, said a spokesman for Scott's office.

The gas tax and the proposed levy on large low-mileage "gas guzzler" cars received the most criticism. "If people disagree, those are the two issues they disagree with," said David Guskey, an assistant to Rep. Glady's N. Spellman (D-Md.)

The complex tax proposals also were the most commonly misunderstood. "All the people heard was 'tax', and that raised their hackles."

They worry they'll be invaded by inspectors . . . and that the tax will happen all of sudded," said a spokesman for Rep. Newton I. Steers Jr. (R-Md.)

"People think the coal conversion (to be required of oil-burning industries) will apply to private homes, too. they think they'll get rebates off their income taxes," said McDonald, of Fisher's office.

"I write because people in Washington seem to despise our having automobiles," wrote a Norfold constituent of Sen. Scott. "Protect us from this taking away of our freedoms: conserving didn't make this nation great. Producing made it great."

"People get into what kind of car they drive, their work schedule, how many kids they have to take to school, go on vacations and that sort of thing," said Sarah Orrick, who handles legislatives mail in the office of Sen. Paul S. Sarbarnes (D-Md.), "The thrust is that the tax would discriminate against the middle class and force people in rural areas to spend much more money getting to work," she said.

Carter won points from many letter writers for raising the energy issue in the first place, but then they criticized him for things he forgot.

"You can't pack a family of six or seven into a Volkswagen. You need to address Detroit a little more firmly," a correspondent wrote to Rep. Spellman.

"Resist any temptation to tamper with the program except to make it more stringent," one person wrote Rep. Herbert E. Harris. (D-Va.)

Several congressional offices reported public concern with the plan's ommission of benefits for mass transit. "They're only car-oriented in Prince George's County because there's no transit out there," said Terry Schuette, Rep. Spellman's press secretary.

Some who wrote to Rep. Barbara A. Mikulski (D-Md.) calling for higher taxes on recreational vehicles as an unneeded luxury and asking for more tax breaks for solar energy units. "Some older citizens were very much in favor of (gasoline) rationing," said Sandra Stafford, of Mikulski's office. "They've been through it (during World War II), and they think it's fair."

Administration officials have said rationing would present colossal administrative problems and could create a black market in gasoline. When rationing was mentioned in recent letters, it was mentioned favorably.

Both Northern Virginia congressmen, Fisher and Harris, reported concern from homeowners who installed insulation before April 20 and therefore would not receive rebates available under the proposed bill to those who insulate after that date.

Other suggestions called for abolition of instant-on television sets that use energy while they are turned off, the closing of all-night shopping centers and an end to night activity at race tracts.

"The President said nothing about giving up his helicopter or members of Congress giving up their trips," wrote a constituents of Sen. Sarbanes, without elaborating.

Illustrating the tendency to be very specific, a seventh grader wrote from Warrenton, Va., to Sen. Scott: "I'm concerned about the problem of large car-owners. My father is 6 feet, 5 inches tall, and he is too tall to fit in the smaller gas-saving cars. Should he be penalized for his size by paying more money.?"

They youngster asked that a person's size be considered when restrictions on the size of cars are enacted.