ANNAPOLIS -- On the surface, Maryland's Tuesday primary is approaching with barely a ripple.

Democratic incumbents, led by Gov. William Donald Schaefer, are prohibitive favorites for the statewide offices at stake this year, and leaders of both political parties predict a paltry turnout.

But there is more at risk than meets the eye when the polls open for the state's 1.33 million registered Democrats and 606,000 Republicans. Their choices could set the stage for a substantial turnover in the state Senate, produce at least one new face in Congress and decide the leadership of several suburban counties.

Tuesday's voting also will be an important test of voter sentiment on abortion, which is a central issue in at least six state Senate races, four of them in the Washington suburbs, as well as the race for the congressional seat of Democratic Rep. Roy P. Dyson, an abortion opponent.

The results may not be epochal: The state election four years ago offered a more profound change in the Maryland political landscape, producing a new governor, a new attorney general, a new U.S. senator and four new members of Congress.

Yet the stakes are still significant for everyone from Schaefer, who has waded heavily into the Democratic primaries on behalf of some struggling incumbents, to the special interest groups that have poured a record $2 million into state campaigns.

Anti-incumbent sentiment has caused an unexpectedly stiff challenge to Montgomery County Executive Sidney Kramer, and put more than a dozen of the state Senate's 47 seats within the reach of challengers. Schaefer has picked favorites in many of those races, a gamble that could earn him either a more compliant state legislature or a new crop of enemies.

"The down side is something I am sure he {Schaefer} can calculate very well," said Tom Cowley, executive director of the state Democratic Party. "I think the down side turns out to be minimal, but these are tough choices."

Tuesday's results also will dictate the November gubernatorial lineup. Schaefer in the primary faces Anne Arundel real estate agent Fred Griisser. Republicans will pick either retired foreign service officer William S. Shepard, of Potomac, or retired Baltimore surgeon Ross Z. Pierpont.

Of the two, Shepard has run the most aggressive campaign, issuing position papers and scouring the state for bull roasts and picnics to attend. Pierpont, a perennial and never-yet-successful candidate for state and national office, is relying on name recognition from 10 previous campaigns and voter dissatisfaction with Shepard's unorthodox choice of his wife as a running mate.

Among the candidates with the most to lose is Kramer, whose incumbency and future as a possible gubernatorial contender are endangered by veteran County Council member Neal Potter. Potter has made a close race out of a challenge dismissed early on by some as simply a protest of what Potter sees as Kramer's pro-development leanings.

Incumbents on the all-Democratic County Council also are running hard, pursued by challengers from within their party and Republicans encouraged by the expansion of the council from seven to nine members.

In Prince George's County, two entrenched incumbents, County Executive Parris N. Glendening and U.S. Rep. Steny H. Hoyer, are being tested by challengers. Glendening faces County Council member Floyd E. Wilson Jr., and Hoyer is being challenged by Abdul Alim Muhammad, national spokesman for the Nation of Islam, who has made an issue of whether Hoyer has adequately represented the interests of blacks in the district.

Voters in Anne Arundel and Harford counties, where James Lighthizer and Habern Freeman are leaving office, will choose nominees for their county's top posts as well.

Incumbents also are dominating the state's eight congressional races this year. The one exception is the 1st Congressional District, where the reelection chances of 10-year Democratic veteran Dyson have been weakened by the revelation that he was a conscientious objector in Vietnam, a position the hawkish conservative had not revealed until questioned about it by The Washington Post.

His main challenger, Del. Barbara O. Kreamer (D-Harford), has alleged that Dyson's draft status doesn't square with his current pro-defense stands -- he supported pre-positioning of forces in the Middle East and said the use of nuclear weapons should not be ruled out -- and acceptance of campaign funds from defense contractors.

Dyson has said his conscientious objector status was based on his opposition to the Vietnam War, not the moral opposition to all wars that most local draft boards required.

The race, and the eight-way Republican primary contest in the district, have led to a flood of last-minute mail and attack advertising. Kreamer began airing a 30-second television ad that poses the question: "Which Roy Dyson do you believe? The hawkish congressman . . . or the conscientious objector who skipped Vietnam?" Dyson countered with a radio spot characterizing Kreamer as "panic-stricken . . . her failed campaign has turned ugly."

Activists on both sides of the abortion issue also will be watching Tuesday's results closely, with an eye towards strategy in the legislative session. Abortion opponents, who blocked passage of an abortion-rights bill this year with a Senate filibuster, concede that at best they will break even on Tuesday, and probably stand to lose strength in the state House. Late last week, leaders of an abortion-rights group said they had poured an extra $12,000 into three key campaigns in Montgomery, Prince George's and Baltimore counties in an attempt to push three challengers past antiabortion incumbents.

Senate President Thomas V. Mike Miller Jr. (D-Prince George's) said the abortion issue has given credibility to several challengers, bringing the potential for turnover to a typically stable chamber.

"Four years ago, the only people moving up to the Senate were House members when a senator retired," Miller said. This year, "people have issues which they can take to the voters and challenge incumbents."

Tuesday's primary also is important to the state's two main political parties, though for different reasons.

For Republicans, the issue is how to promote party unity and success in the November general elections after an unexpectedly large number of primary races. Party Chairman Joyce L. Terhes said the primaries, along with the 70,000 Republicans added to the rolls since 1988, are proof of the GOP's growth.

For the Democrats, it's a question of whether the party can maintain or increase its domination of the state House and county courthouses in the face of increasing Republican registration.