The Chesapeake Bay, whose polluted waters were ignored by state and federal officials during the past decade, has emerged in this election year as the Reagan administration's favorite environmental cause.

The Reagan administration has endorsed an unprecedented four-year, $52 million cleanup project and some additional monies in separate bills, which Congress is expected to authorize before its scheduled adjournment this week. The bulk of the money commits the federal government to work with states on the project.

Once an environmental issue that languished in the shadow of acid rain and hazardous dumps, the bay cleanup has emerged suddenly as a symbolic project with seemingly no detractors.

"The Chesapeake Bay is now the motherhood issue, and everybody is off getting their blood tested to prove that they're the father," said Betty J. Diener, Virginia secretary of commerce and resources.

President Reagan himself toured the bay this summer, after singling out the cleanup project in his State of the Union address last winter. House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) quickly followed suit, spending two hours cruising its waters in an 82-year-old double-masted skipjack.

And Defense Secretary Caspar W. Weinberger went further in elevating the importance of the bay cleanup, recently describing it as tantamount to protecting "our national security."

Yet federal funding for the bay is small compared to dozens of environmental projects that receive much less attention, such as the $200 million annual federal sewage treatment program.

Nonetheless, the bay's proximity to Washington, combined with a newly released federal study pinpointing its pollution problems, provided the Reagan administration with a logical vehicle to demonstrate the president's commitment to the environment, according to Republican and Democratic congressional staff aides.

"The symbolic effect goes far beyond the monetary impact," William D. Ruckelshaus, administrator of the Environmental Protection Agency, said in an interview last week. "The administration is finally putting its imprimatur on the cleanup of the bay."

Ruckelshaus, who acknowledges that environmentalists are suspicious of the administration, said presidential politics played no part in this year's decision to provide federal support for the Chesapeake.

Republicans and Democrats on Capitol Hill say privately, however, that the Reagan administration needed an environmental issue to restore its credibility after scandals erupted at the EPA under administrator Anne Burford in the first half of Reagan's term.

The bay, used by many Washingtonians and familiar to congressmen of every stripe, was, in the words of a Republican senator's press secretary, a convenient "cheap date."

"Anne Burford has been our biggest help, although not intentionally," said Rep. Roy Dyson, a Maryland Democrat whose district borders the bay. "The administration has been caught in a situation they would rather not be in. All of sudden it looked like the fox was guarding the hen house. Reagan had to offset that."

Area congressmen and Hill staff members credit Ruckelshaus -- whose car for the past 18 months has displayed a "Save the Bay" bumper sticker -- with carrying the torch inside the administration against a resistant Office of Management and Budget.

Armed with a new study, and commitments from Maryland, Virginia and Pennsylvania to match federal funds on the new program, Ruckleshaus was able to persuade Reagan to change his position on bay funding.

"We couldn't get anywhere with Burford," said a Republican aide on Capitol Hill closely involved in the bay issue. "We had no support from the administration . . . . At some point I think Ruckelshaus made the decision to go to bat for the bay."

But even arousing Ruckelshaus' interest was part of a calculated stategy by Sen. Charles McC. Mathias (R-Md.), who for 10 years had struggled for a federal commitment to clean the bay.

A year ago, at the invitation of Mathias and Democratic Maryland Gov. Harry R. Hughes, who has made the bay cleanup a top priority, Ruckelshaus toured the bay. With them were key politicians from the three states responsible for bay pollution, including Virginia Gov. Charles S. Robb, Pennsylvania Lt. Gov. William Scranton, Sen. Paul S. Sarbanes (D-Md.) and Sen. John W. Warner (R-Va.).

For several months afterward the only signal coming from the administration about the prospects for federal funding was strong opposition from the Office of Management and Budget, according to congressional aides. When Mathias and Warner were unsuccessful in repeated attempts to meet with OMB Director David Stockman, rumors began circulating that Reagan had blocked the project, the aides said.

Late last year Jack Svahn, newly appointed domestic policy adviser at the White House, met with Mathias, Warner and other area congressmen to hear their case and assure them that Reagan had made no decision on the bay.

Impressed with the $27 million EPA study that was released a few months earlier and the congressmen's arguments that a clean bay was vital to the states' economies, Svahn said, he took the issue to Reagan.

"The president decided after that that it was well worth the seed money invested to help the states clean up the bay," Svahn said last week.

Also key, according to Ruckelshaus and others, was the commitment by Maryland, Virginia and Pennsylvania to spend millions of dollars in state funds on the project. "The taxpayers of adjacent states are putting up their revenues and Uncle Sam could do no less than match," said Warner.

With momentum building, the strong state commitments helped deliver the coup de grace -- inclusion of the bay in the State of the Union address last January -- a symbolic effort strongly pushed by Ruckelshaus, Mathias and other area Republicans.

"This presents an ideal opportunity for the administration to demonstrate its awareness of the environment and, at the same time, show how its New Federalism program has been a working success," Mathias wrote in a letter to Svahn as the president prepared the speech.

Ruckelshaus said the bay "was in and it was out" of the speech at different points. In the end, Ruckelshaus said, its brief inclusion "was terribly important" and had a snowball effect in heightening awareness about the bay at other federal agencies. More funds for the bay were added to the budgets of the Departments of Interior, Agriculture, Defense, the National Oceanic and Atmospheric Administration and the Army Corps of Engineers.

The issue also provided ready political capital for area politicians. At one ceremony, Ruckelshaus recalled, a number of Virginia state legislators were delighted by the horde of reporters who was covering them and the event.

Afterward, these same legislators, said Ruckelshaus, were "falling all over each other" to spend more money on the bay than was included in Robb's budget, surprising the governor, who expected resistance from the fiscally conservative General Assembly.

Even an announcement that Reagan would mention the bay in the State of the Union address had a political tinge.

Mathias' office learned the news first. But Warner, who is running for reelection, announced it to the news media the day before the speech.

Apart from this minor incident, supporters of the bay generally have shared credit for this year's achievements. Ruckelshaus, noting that the cleanup effort hinges on the cooperation of many states and federal agencies, warned that future finger-pointing and credit-grabbing pose the greatest threat to the success of the project.

"Everybody is in favor of this in the abstract," Ruckelshaus said. "The crucial thing in my view is that the parties recognize that we're all in this together. The minute we start dragging our feet and pointing the finger it could all fall apart."

"The time to claim credit is 10 years from now," he added. "That will be the time to crow about it."