There was a better survival rate among incumbent members of the Maryland General Assembly from Montgomery County than elsewhere in the state in last week's primaries, which set the stage for general election races between Montgomery's entrenched senior legislators and another round of challengers.

Only three incumbents -- two senators and one delegate -- did not run for reelection, and the remaining 22 legislators were renominated. There are 25 county seats.

By contrast, about 40 legislators from around the state, some of them committee chairmen, fell to primary challenges Tuesday -- a circumstance that is likely to lead to a major reshaping of the legislature in January.

While victory was sweet for the incumbents in the county, and for some meant a guaranteed seat in the legislature, for others it was not easy. In a few cases, the race that ends Nov. 2 could be a rough one.

In particular, Democrats say they intend to add to their overwhelming majority (there are more than two registered Democrats for every Republican in the county) by hanging the Reagan administration's record around the necks of three incumbent Republicans.

The Republicans' strategy includes knocking on more doors than their opponents and out-attacking some of the more vulnerable Democrats by sticking to state and local issues and avoiding federal politics, according to county GOP chairman Paul Clark.

The Republicans plan to concentrate on the more conservative 15th, 16th, and 17th districts, Clark said. Because of the heavy Democratic concentration and small number of Republican candidates, Democrats nominated in the 18th, 19th and 20th districts are considered guaranteed winners. Among those Democrats are Sen. Margaret Schweinhaut and Dels. Donald Robertson, Helen Koss, Lucille Maurer and Joseph Owens.

"Don't ask me about the 18th, 19th or 20th. They're as good as lost," said Clark. "And, in some camps, there will clearly be an adverse effect [from Reagan administration policy] wherever federal employes live.

"But I am convinced that at the state level, whoever does the grunt [nitty-gritty campaign] work will get elected."

Here is how the legislative races are shaping up in the three Montgomery districts -- 15th, 16th and 17th -- where incumbents are facing stiff challenges.

District 15: Incumbents could face some of their toughest fights in this affluent western end of the county, which includes the more conservative Bethesda and Potomac areas. Democrat incumbents Sen. Laurence Levitan and Del. Jerry Hyatt and incumbent Republican Del. Robin Ficker hold seats believed to be vulnerable.

Levitan, a lawyer who is still reeling from an aggressive and close primary fight against Anthony Puca, could be in trouble in his race against state GOP chairman Allen Levey. Levey, a dentist and political moderate, beat hard-line conservative David Bastion in the primary.

Levitan, the chairman of the Senate Budget and Taxation Committee, squeaked through the primary with 56 percent of the vote after Puca criss-crossed the district accusing him of dirty campaign tactics and of conducting personal business in the legislature.

On the House side, the race for three seats is expected to shape up among five of the seven candidates: Democrats Judith C. Toth, Hyatt and Gene W. Counihan and Republicans Ficker and Jean Roesser. Toth, by most accounts, is assured reelection, but the strong showing of nonincumbents during the primary is considered an indication that the remaining seats could be up for grabs.

Incumbents Hyatt and Ficker trailed Counihan and Roesser in their respective primaries.

Hyatt, an attorney, and Counihan, a school administrator and former central committee member, are both counting on an "anti-Ficker" vote to pull them through the election.

Ficker, a maverick, was initially considered a sure winner, but throughout the past year has been losing GOP support, partly because of his publicity-seeking antics, a high party official said.

Meanwhile, the GOP is looking at Roesser, a central committee member and former president of the Federation of Republican Women, for its best chance of gaining a seat.

The other Republican nominees are Jean Cryor, a former campaign organizer and journalist, and Braden Keil, a commodities broker.

District 16: In this affluent district, which includes Friendship Heights and Chevy Chase and which has the highest number of Republican voters, Republicans are hoping to hold on to the seats of Sen. Howard Denis and Del. Constance Morella and to elect House of Delegates candidate John Perrin, a strong campaigner who lost by 200 votes in 1978.

The Democrats, however, think Brian Frosh, a young lawyer, has a good chance of knocking off Denis. Denis won by only a 200-vote margin in the 1978 election, and Frosh has the advantage of strong county connections and name recognition: his father, Stanley B. Frosh, is a circuit court judge and former member of the County Council.

In the delegates' race, incumbents Morella and Nancy Kopp are considered safely ahead, leaving Gilbert Genn, a lawyer and longtime party worker, and incumbent Marilyn Goldwater, both Democrats, and Republican Perrin in the strongest position for the third seat. Genn already has a strong organization lined up.

The other Republican nominee for a House seat from this area is Gary England, an engineer.

District 17: Former Rockville City Council member Phyllis Fordham, a Republican, should give incumbant Frank Shore a good run for the Senate seat from this district, which includes Rockville and Gaithersburg, but most political observers expect Shore, an inveterate campaigner, to win. Shore is an anomaly in county politics, tapping the church vote and organizations such as the Elks, whereas Fordham is expected to go after a broader base of support.

Republican Stephen Abrams, a current member of the Rockville City Council, and Democrat Michael Gordon will battle for the one open seat in this district, that vacated by Del. Luiz Simmons in his unsuccessful bid for the county executive's job. Incumbent Democratic delegates Mary Boerghers and Jennie Forehand are expected to win the other two seats.

Republicans Stephen Eckles, a former party county chairman, and Richard Frederick, a lawyer, round out the GOP's House ticket.