The Washington Monument grounds will be transformed into a giant sundial Wednesday to mark the hours of a dawn-to-dusk extravaganza known as Sun Day, a nationwide celebration of solar energy.

Sun Day, a solar successor to Earth Day, will be greeted at daybreak at the Lincoln Memorial with sunrise ceremonies punctuated by the rising of a hot air balloon.Here and across the nation, there will be bike tours, fairs, picnics, rallies and technological exhibits, ranging from solar-powered water heaters and solar-generated electricity to traditional windmills.

The Sun Day spectacular has been organized by a coalition of environmentalists, politicans, consumer activists, labor unions and others, including some of Earth Day, an environmentalists' celebration that took place April 22, 1970.

Earth Day, a day on which Americans rallied to clean up litter, bemoan air polllution and push for conservation, has widely been cited as an event that helped usher in an American era of environmental protectionism, including major antipollution legislation and establishment of the Environomental Protection Agency.

For Sun Day in Washington, the National Weather Service, appropriately, has tentatively forecast mostly sunny skies with cool temperatures expected to reach the high 50s during the afternoon.

Sun Day is intended by its organizers to herald a new era of public awareness about solar energy's promise and to spur the federal government toward increased investment in solar technology. Although Sun Day's sponsors have sought to avoid any gloomy notes, the celebration appears, nevertheless, to have a decidedly antinuclear flavor and it will take place amid continuing controversy over the Carter administration's solar energy policies.

While President Carter and many other government officials plan to take parts in Sun Day ceremonies, the Carter administration has increasingly drawn criticism from environmentalists, consumer advocates and others, who contend that Carter has neglected the solar option. The administration's energy policies, istead, have stressed coal and nuclear power.

Solar energy - in many respects still in its infancy in the United States - is currently caught in an array of technological, economic and political uncertainties. The questions reach from the meeting rooms of environmental groups to the White House and federal agencies. The questions also are being asked in Congress, where significant solar legislation is under consideration, and in corporate board rooms and manufacturing plants where research and production of solar equipment are increasingly being discussed and carried out.

The central issue in much of the national debate has been now rapidly the United States should move toward making more use of solar energy. Most environmentalists contend that the nation is moving too slowly toward increased reliance on what they view as a safe, secure and pollution-free energy source. Many government officials express a considerably more cautions outlook, arguing that solar energy may have long-term promise but that it faces severe short-term obstacles.

Viewed from these conflicting vantage points, solar energy has recently prompted a spate of accusations and disagreements among environmentalists and government officials.In an interview over the weekend, Denis Hayes, an environmental researcher and key orgainzer of Sun Day, complained about what he described as the Carter administration's neglect of solar energy thus far. "There's been no zip," he said. "The whole thing is mainly business as usual."

As evidence of the Carter administration's lack of support for solar energy programs, Hayes cited a $10 million cut in the administration's proposed 1979 budget for solar projects below the 1978 spending level, Carter's failure so far to fill the position of assistance secretary of energy for conservation and solar applications, and opposition by federal agencies to a congressional proposal to create a social lending institution to help finance solar energy ventures.

A differing viewpoint was expressed by Donald A. Beattie, who temporaryily holds the job of acting assistance energy secretary for conservation and solar applications. In an interview, he expressed concern that Sun Day might cause "overexpectations" about immediate prospects for solar energy. "In my opinion, its not (now) the answer to our energy problem. It may be the answer in 50 years," he remarked. Beattie, nevertheless, said he regards Sun Day as an encouraging development.

There have been several recent indications of increased federal emphasis on solar energy's prospects. The White House's Council on Environmental Quality issued a report last month concluding that the United Sates could obtain up to a quarter of its energy supply from the sun by the end of the century. The White House is also preparing, accoding to administration sources, to appoint a high-level panel soon to press for solar energy development.

In Congress, 27 senators and 67 representatives have formed a solar energy lobby, known as the Solar Coalition, to push for a legislative package, now including 13 bills. Their results so far appear to have been mixed. Among the coalition's proposals is a $35 million program of Small Business Administration loans to help finacne installation of solar equipment and the creation of a $5 billion Solar En-energy Bank other or similar fund. The latter proposition was opposed by federal agencies in recent testimony.

The House Science and Technology Committee has also tacked an additional $160 million onto President Carter's solar energy appropiations request. One key solar energy plan - Carter's proposal for tax credits of up to about $2,000 for homeowners who buy solar systems - has remained trapped in a year-old congressional stalemate over Carter's overall energy plan.

Although solar-powered devices have only recently begun to gain acceptance among American homeowners, the National Solar Heating and Cooling Information Center, a government-financed group, has reported that 40,000 buildings throughout the nation now are equipped with solar heating systems. Most of these, a center official said, are water heatingdevices. About 5,000 American homes are estimated to use solar equipment for general interior heating, the official said.

Today, there is a wide array of solar-powered equipment available for homes, businesses and special industrial and scientific uses, ranging from relatively simple devices to others that are extraordinarily complex.

One form of solar home-heating system rallies on collectors, usually attached to the roof of a house to absorb the sun's energy and transmit it indoors by water through pipes. Another system, known as "passive" solar heating entails use of architectural designs allowing direct sunlight to warm the interior of a home. Solar-generated electricity usually employs extremely costly techniques relying on what are known as photovoltaic cells, often made of sillicon.

Such major U.S. corporations as Grumman Aerospace Corp. and General Electric Co. have already begun manufacturing solar collectors for home heaing, a possible indication that solar technology may soon spawn a booming industry.

In the Washington area, only about 50 buildings are equipped with solar-powered devices, according to some solar energy advocates. They range from a scattering of private homes in Cleveland Park, Capitol Hill, Georgetown and Bethesda to such publicized ventures as the Terraset School in Reston, an experimet financed by the Saudi Arabian government.

"I think D.C. is a good place for solar but I don't think the word has gotten out yet. No big builder has taken it up and the financial institutions aren't plugged in," Joan Storey, one of the Washington area coordinators for Sun Day, said yesterday. "Everyone is waiting for the feds to take the initiative."