One Saturday not long ago, the three incumbent Democrats from the 16the House of Delegates District in Montgomery County and their volunteers knocked on every door in Garrett Park. Their campaign maneuvers, like that of their three Republican opponents, are a war on foot.

In Friendship Heights, Westmoreland Hills, Garrett Park, Bethesda, Kenwood and Chevy Chase, where some of the county's best-educated, richest and most independent voters live, incumbents and challengers start out "even," in the legislative race, said incumbent John X. Ward.

Once elected, incuments cannot rest. In the 16th District, a seedbed of civic activism, each election year is a stern test of responsiveness.

The situation is only heightened by the tradition of electing Republicans. In the 16th District "voters like to split their tickets" to show their independence, one precinct official said.

"What we emphasize," said Ward of the incumbent House team, "is our four years in the legislature and long involvement before that in the community - to show a continuum of service."

Ward and the other two incumbents, Marilyn Goldwater and Nancy Kopp, are campaigning collectively in the face of a determined GOP challenge from Connie Morella, Graham Weaver and John Perrin, who intend to pick off at least one Democrat.

In the 16th District Senate race, incumbent Howard Denis, a Republican who was appointed to the seat two years ago, is campaigning against Joe Gebhardt, a Democrat and public interest lawyer.

The Democratic delegates have a record of joint service.

Goldwater, a nurse, has focused on health, social and consumer legislation. Some of her successful bills have included establishing safety guidelines for DNA research, day-care centers for the mentally handicapped, insurance coverage for nurse midwives and flex-time employment programs.

Kopp, a political scientist, is chairman of the Legislative Study Group, a group of legislators bent on "reforming" the legislative process. She has promoted "sunset" legislation, requiring periodic review of state programs, and has led a fight to require recorded committee votes and advance public notice of meeting and voting sessions. "Government effectiveness is not a very sexy issue, but it's very important," she said.

Ward has sponsored what he calls "common sense" legislation - including a "single license plate" bill he says would save the state $2 million over a five-year period. The bill failed last year, but Ward said he will try it again. He has backed tenants' rights and consumer legislation, such as bills requiring local public hearings for utility rate increases and efforts to "bring some modification to the gluttonous insurance industry."

Gebhardt, according to Kopp and Ward, would "strengthen" the 16th District legislative team by offering four Democrats in a Democratic-controlled legislature. Gebhardt, who was a Udall delegate to the 1976 Democratic National Convention, is campaigning on a platform that stresses ethics and campaign finance reform, the clean-up of the Potomac River, stronger controls on property taxes and utility rates, the need for a state consumer advocate, better recycling and environmental laws and protection of tenants.

But Denis, the Republican incumbent, said he can offer "performance, not promises.

"I voted against the increase in sales tax and in the country piggyback income tax," he said. "I was consistently for lower state budgets. I also voted against a lot of marginal projects - a new symphony hall and renovation of the Lyric Theater and Memorial Stadium (all in Baltimore)." He is a backer of ethics legislatin and a bill to require covers on dump trucks (it passed the Senate but not the House).

Of the Republican House candidates, Connie Morella, who narrowly lost the contest in 1974, said she will work to eliminate red tape that hampers businesses, for tax reform, for regulation of public utilities to ensure equitable rate structures that would encourage energy conservation and for increased opportunities and financial security for older people.

"We need to get a greater return from the state for Montgomery County," she said.

Graham Weaver, the county's Ford and an insurance of Edgewood-Glenwood Citizens Association and legislative cochairman of the Montgomery County Civic Federation. Locally, he has worked to block income tax increases. Weaver said he supports a "substantial" increase in the standard income tax deduction to help renters as well as homeowners, legislation to prevent child abuse and the use of tax credits to assist the handicapped.

The third Republican, John Perrin, also an unsuccessful candidate in 1974, is chairman of the county Consumer Advisory Board, a precinct official and former president of the Hillmead Citizens Association. He favors increased economic development in the state, a reduction in state government employment and a stabilizing of property taxes by restricting the frequency of reassessments and increases in assessments above the rise in the cost of living.