A quest for 'open space' near bustling Silicon Valley.

Mel Wright is an old hand at exploring the nooks and crannies of the coastal range, which starts to rise about four miles west of this Santa Clara Valley town. His acquaintance with the area goes back to 1948, when he was one of the original four rangers in Big Basin State Park. An engineer by profession, he has made a pastime of getting to know the wildlife in the lands just beyond Silicon Valley.

''I like to get away from the city,'' he says. ''I like the flowers, I like the open hills. The poppies and trilliums are spectacular in the spring. You can drop down into the upper part of Stevens Creek from the Monte Bello Preserve - that's the area where you run into these wintering-over, waking-up swarms of ladybugs. I actually like the new foliage on the poison oak.''

Mr. Wright was also an early supporter of public acquisition of lands in the coastal range, through an organization known as the Mid-Peninsula Regional Open Space District (MROSD). Established by voters in 1972 in response to heavy residential and industrial development, the MROSD uses money from local property taxes and other sources to preserve wild lands in the foothills of Silicon Valley and in the San Francisco Bay Area lands - an area that has seen rapid, often uncontrolled growth over many decades. The latest burst came with the high-tech boom of recent years.

With an annual budget of about $13.8 million, MROSD derives 41 percent of its income from a voter-approved assessment of property within the district, costing the average homeowner about $13 a year. Federal and state grants and interest on income, as well as outright gifts and bequests, augment the district's buying power. Despite skyrocketing land values - a little over half an acre can sell for $350 thousand in some Silicon Valley communities - the district has managed to increase its holdings in the last seven years from 6,000 acres to about 18, 000 acres. It offers 60 miles of hiking trails spread over 24 preserves - all open to the public as well as to the residents of the district. It is one of only three open-space districts in California, and one of a handful in the nation.

''Each of us who supported the open space plan had known the disappointment of losing lands that were important to us,'' says Nonette Hanko, one of the founders of the MROSD and a current member of the district's board of directors. ''I moved to Palo Alto in 1951, and in only a few years I watched all the poppy fields and fruit orchards disappear.''

As Craig Britton, land acquisition manager and assistant general manager of the MROSD, explains, the goals of the district are twofold: to set aside individual parcels of undeveloped land for public use, and to link as many of those parcels as possible to provide an uninterrupted stretch of open space.

''We're really trying to create an urban greenbelt,'' Mr. Britton says. ''We're trying to provide places for quietude and serenity, for peace of mind.

''We're also preserving future options. If we'd let it go the way it was going, in another 20 years there wouldn't have been any undeveloped land.''

The MROSD, which now includes a 25-member staff, a board of directors, and a team of 60 docents, began its existence as a question on a public survey in 1970 . Supporters of an open-space plan, including volunteers from various groups - the League of Women Voters, the American Association of University Women, the Sierra Club, Friends of the Foothills, and others - polled 4,600 residents in 20 south Bay Area communities to find out who would vote for the formation of a regional open space district.

''1970 was just the right time for something to work out (for land preservation),'' says Ms. Hanko. ''The people of the area all knew what was happening.''

The open-space survey revealed that 73 percent of the residents would vote for the district. Supporters of the district then gathered the necessary signatures for a ballot initiative, gaining approval along the way from the Santa Clara County Local Agency Formation Committee and the Santa Clara County Board of Supervisors. The formation of the district came up for a vote in the county in the general election of November 1972, with voters approving the district by more than a two-to-one margin. After overcoming a legislative challenge to its taxing authority, the district began to purchase undeveloped land in 1973.

The voters of southern San Mateo County, adjacent to Santa Clara County, voted to be annexed by the district in 1976. The present district boundaries, which encompass cities as well as undeveloped lands, created a potential stretch of open space nearly 40 miles long, from the city of San Carlos, about 20 miles south of San Francisco, to an area several miles southwest of San Jose.

The district is not without its controversies. Its large number of users often have differing ideas about the purposes of the land - particularly about how much recreational development should be allowed.

''We're at a very interesting point now,'' says Charlotte MacDonald, editor of the district's newsletter, ''because we're not only being asked to provide a lot more facilities, but we have begun to provide more facilities. The issue is how much like a park district we're going to become.''