The grass in federal parks will be longer this summer, the flower beds weedier, the statues dirtier, the parkways and horse trails more full of holes, the hydrilla less closely monitored and the Park Service rangers less available to visitors on the Mall as the new deficit reduction act goes into effect in the Washington area.

The first round of a 4.3 percent reduction in the federal budget began March 1 and amounts to a ripple compared to the tidal wave of cuts required under the law in October.

National Park Service Director William Penn Mott said the Gramm-Rudman-Hollings Act may force some of the nation's 330 national parks, historic sites and recreation areas to close next year. But no closings in the nation's capital are currently under study.

"We tried to avoid the Washington Monument Syndrome," where a federal bureaucrat announces extremely unpopular actions to pressure Congress into restoring the money, said Manus (Jack) Fish Jr., director of the Park Service's National Capital region. "The grass may be a little bit longer, but everything will be open."

"Yes," he said, "I think the public will notice."

Included among the most obvious signs of budget-cutting will be a 50 percent reduction in the number of potholes filled in the Baltimore-Washington Parkway, 45 fewer U.S. Park Police than planned, fewer patrols on the Mount Vernon bike trail, no new furniture for Arlington House and fewer portable toilets along the George Washington Parkway. There also will be reduced lighting around the Visitor Center at Great Falls Park, no cleaning of the tunnel at the National Zoo, no tours of the site of the Second Battle of Bull Run and three miles of unmowed grass along the fence at the Manassas National Battlefield Park.

"We had to look at what is most important to visitors and make the cuts in what seemed to us to be the fringe areas," Fish said. "The park superintendents will have to watch each thing and if conditions get too bad they may have to go and cut somewhere else."

Under the Gramm-Rudman-Hollings deficit reduction act, the $85 million regional parks budget was cut by about $4 million, line item by line item.

The act requires across-the-board automatic cuts in each budget item every year -- unless Congress makes equivalent reductions -- until the nation's almost $200 billion annual deficit is eliminated in 1990.

Cuts similar to those in Washington are being made in every park in America, with maintenance reduced, landscaping cut back, equipment purchases and repairs deferred and rangers not hired.

"The cuts are significant, and a very big mistake," said Destry Jarvis, vice president of the National Parks and Conservation Association. "Visitors to the parks this summer will have a diminished experience as a consequence. Unfortunately the Park Service has virtually no flexibility in making the cuts."

About 20 percent of the 250 normal summer positions in Washington's federal parks will not be filled this year.

The number of seasonal employes who watch over the Mall and offer visitor assistance at the Washington Monument, Lincoln Memorial and Vietnam Veterans Memorial will be reduced from 22 to 15.

"Visitor assistance and the protection of the monuments will be reduced," Fish said, "but we felt this was better than reducing hours." Grounds maintenance around the monuments will be cut by about one-quarter and trash pickups and lawn mowing will be less frequent.

Grass, flower beds and other plantings near the benches on the Ellipse where summer visitors queue up for White House tours will be allowed to deteriorate because the working hours of gardeners will be reduced.

Some major events in all Capitol Hill parks and in Anacostia Park will be unstaffed, and a program to eradicate a rapidly spreading weed called kudzu will be cut back.

Trash will no longer be picked up on Thursdays and Fridays in Rock Creek Park, where Park Service employes are being placed on a permanent schedule of Saturday through Wednesday. Grass will be mowed every 20 days instead of 15.

"Results will be an unsightly appearance of tall, uneven grass in highly visible areas such as Meridian Hill Park, Rock Creek and Potomac Parkway, Battery Kemble Park, Rock Creek Park, Fort Reno, Canal Road and P Street," according to Gramm-Rudman-Hollings impact statements prepared by park officials.

About 120 storm drainage basins along roads in Rock Creek Park will not be cleaned, possibly creating some road flooding and shoulder erosion, the impact statements say. The unsightly, dirty condition of the 800-foot tunnel at the zoo will continue because it will not be cleaned at all during 1986.

Additionally, the mowing cycle will be cut back along Wisconsin and Massachusetts avenues, and at Ward, Tenley and Chevy Chase circles. Holes in horse trails will not be repaired. No holiday or evening programs will be offered at Old Stone House, Pierce Mill or Rock Creek Nature center.

The Theatre in the Woods program at Wolf Trap Farm Park will be cut by two weeks and all morning shows will be eliminated. Fewer ushers will be hired for the Filene Center. Maintenance and mowing, watering and weeding will be done less frequently on the grounds.

Money to continue a 30-year program of repairing the Anacostia River and Washington Channel sea wall will be eliminated, and at the Harpers Ferry National Historical Park, fewer buildings will be staffed.