Once again is Howard County Md., the Marriott Corporation is pitted against people worried about keeping their air clean, their roads uncongested and cotton candy-eating tourists out of their back yards.

The fuss is over plans Marriott is pressing for the second time in five years for an amusement park. The pack would be built on 220 acres of a vacant 500-acre plot along Interstate 95 about 5 miles east of Columbia.

Only this is not the usual kind of amusement park. Designed in the new tradition of what are called "theme parks," this one would have more rides than a bunch of county fairs put together, more hometown-style restaurants than most American towns, and more laughs and thrills than a circus. In fact, it would have its own circus.

Yesterday, several hundred people wanted patiently inside the Atholton High School to testify before the Howard County Zoning Board that the last thing the county needed was a circus. They brought with them a petition signed by 3,851 residents objecting to the park.

Outside, on the steps of the high school, a throng of antipark activists passed out red decals saying "No To Marriott Again" and a single page statement that read, in part:

"We will not become the 'sand box' for the megalopolis of the Northeast. There are alternate ways to develop our county while we protect our quality of life. Let it not ever be said that Howard County is a nice place to visit but I wouldn't want to live there."

Marriott officials say the proposed park will actually make Howard County a nicer place to live. In testimony taken by the zoning board last week, engineers consultants, attorneys and J.W. Marriott Jr. himself - president of the Bethesda-based firm - stressed these positive points about the park:

Employment. Marriott will have to hire 3,000 teen-age and college-age people to operate the park during the summer, plus 200 part-time adults and 300 full-time adults. Many of these hires will be drawn from the Howard County area, officials said.

Tax revenues. The park will generate $3 million in property, admission and amusement taxes. It will cost the county an extra $441,000 in police, fire, environmental health and administration expenses. The net surplus to the county would be $2.6 million.

Fun and entertainment.

Marriott itself is new to the amusement park business. Traditionally, it has been a hotel, restaurant and catering company. But last year, in an expansion which many on Wall Street regarded as risky, the firm opened two parks in Gurnee, Ill. and Santa O'lara County, Calif. Called "Great America Theme Parks," the proposed Howard County park has been modeled exactly after these.

Both ventures proved to be enormously successful financially and, according to Marriott officials, people living in surrounding communities who initially opposed the projects, now welcome them.

The Howard County opposition, said it wasn't concerned with what has happened elsewhere. "Each and every geographic spot in these United States is indeed different," said S.C. Hartman, management consultant and leader of the loosely organized coalition, Concerned County Citizens, Inc.

Other coalition members called into question Marriott studies that say the proposed park will cause minimal congestion in the area because most people will use 1-95 to get to it. They also challenged engineering reports indicating the park will not be an overriding burden on the county's water, sewage and solid waste disposal systems.

They asserted that cars driving to and from the park would raise air pollution in the county to unhealthy levels. And quoting police figures from Orange County, Fla. - which show that crime increased 70 per cent during the five years after Disney World opened - they predicted similar results in Howard County if the park opens.

"I came here specifically to get away from crime, pollution and traffic," said Robert Sokolove, an attorney for the Department of Housing and Urban Development who recently moved to Howard County from New Hampshire. "What this park would do would bring the problems to me. I might as well leave Columbia and go to Washington and experience the same problems."

Summarizing all the objections, Hartman urged the zoning board: "Find an enterprise more in keeping with the established zoning and land use traditionally the standard, one which would cause the rest of us less vulnerability to the chances of life style changes."