The Department of Interior has approved a third grant of more than $1 million for Montgomery County's largest and one of its least-known parks, Seneca State Park, which stretches 12 miles from Gaithersburg to the Potomac River.

Seneca is expected to open unofficially this winter, with formal dedication to be held sometime next spring. The 6,600-acre park has been closed to the public for most of the 25 years the state has been buying the land because it contained few roads and has had no public facilities.

The 90-acre flood-control lake -- stocked with bass and other gamefish three years ago -- if the third largest in the county after the two 800-acre Triadelphia and Rocky Gorge reservoirs on the Howard County line. The Maryland Park Service had hoped to open the park last summer but was delayed by problems in constructing roads, buildings and sewer lines to the main picnic area and marina, according to James Mallow, state parks administator.

The state park will be open this winter for ice skating and ice fishing, as well as for sledding and cross-country skiing, park manager Clifford Denney said.

Summer attractions in the park will include facilities for boating, fishing, hiking, biking and picnicking. The entrance will be on Clopper Road, west of Gaithersburg.

The $1,075,700 grant to Seneca, and a $291,700 grant for the Merkle Wildlife Management Area in Prince George's County, and part of $2.1 million in federal Land and Water Conservation Fund matching grants Maryland will receive during the coming fiscal year.

Last year two grants totaling $3.2 million were given to Seneca. The federal program has provided Maryland parks with more than $40 million since it was established in 1965.It funnels revenues from the leasing of federal lands, such as offshore oil leases, into the purchase and development of parkland across the nation.

The Merkle grant will be used to build a visitor's center at the Canada goose wildlife refuge on the Patuxent River south of Upper Marlboro. The refuge now is inaccessible to the public. The visitors' center and entrance, off Groome Road, will take from two to three years to build, according to Bernard Halla, director of the state Wildlife Administration.

County plans now are being completed for an even larger Montgomery County lake at Seneca Regional Park, downstream from the state park near the town of Boyds. The County Council last year approved creation of a milewide, 452-acre lake at the regional park, which will act as a reserve water supply for the county as well as a major recreational lake. It will hold more than 3 billion gallons of water which, in a drought, could be released into the Potomac River above the county and City of Rockville water intake pipes off River Road above Great Falls.

The 1,862-acre regional park -- now mostly roadless woods and closed to the public -- is expected to take about four years to complete. The park entrance will be on Clarksburg Road (Rte. 121), which will be relocated on a bridge and causeway at the north end of the lake.

Fishing and boating will be permitted in both lakes, although only electric motors will be permitted on boats. Swimming will be prohibited in the state park but may be permitted in the regional park.

Seneca is the first state parkland in Montgomery County to be developed for recreational use. The Patuxent River State Park along the county's northern border with Howard County is not expected to be developed for at least another decade, according to state park officials. More than 6,000 of its planned 7,980 acres already have been acquired.

Last year's federal grants to Seneca State Park permitted the purchase of 1,000 additional acres and the first phase of the park's development -- boat docks, visitor and administration buildings and roads along the north side of the lake. The latest federal grant will permit similar day-use development of the south side of the lake. Development costs of the park, with 50 percent coming from state matching funds, will total about $4.3 million.