Baltimore Mayor William Donald Schaefer and Rep. Barbara A. Mikulski enjoy commanding leads over their opponents in the Democratic primary races for governor and U.S. Senate, according to a Washington Post poll of Maryland Democrats.

Six months before the Sept. 9 statewide primary, Schaefer holds a 3-to-1 edge over Maryland Attorney General Stephen H. Sachs. Mikulski leads her nearest challenger, Gov. Harry Hughes, by 2 to 1 and holds a more than 3-to-1 lead over a third candidate, Rep. Michael D. Barnes, whose district includes most of Montgomery County. Baltimore County Executive Donald P. Hutchinson is a distant fourth.

The results of The Post poll, conducted last week among 599 potential Democratic voters across the state, show that Mikulski and Schaefer enjoy wide and deep support among voters of different sex, race, ideology, age and income. Two-thirds of respondents who say they favor Mikulski and Schaefer categorize themselves as "strong supporters" of the two Baltimore politicians.

Such strong support indicates that their opponents face uphill battles, even if they become better known through advertising and campaigning, unless Schaefer and Mikulski somehow stumble or are sullied during the coming months. The poll also indicates that the 10-month-old savings and loan crisis in Maryland has damaged Hughes' chances in the Senate race, but not necessarily fatally.

Hughes conceded during an interview last week that he needs "to counter to some extent a lot of what has happened over the last several months by getting the proper message out about the savings and loan crisis and how we handled it."

Hughes said his success in the governor's race four years ago was attributable in part to his ability to inform voters about his achievements. This year, he said, his campaign faces a similar challenge in educating voters about his administration's accomplishments, which he termed "some of the best-kept secrets in the state."

In the governor's race, which Schaefer is expected to enter formally this spring, the four-term Baltimore mayor leads Sachs 59 percent to 19 percent. Schaefer is regarded favorably by 63 percent of voters and viewed unfavorably by 9 percent. Sachs is viewed favorably by 41 percent and unfavorably by 12 percent, with 47 percent offering no opinion.

No candidate or state public figure recorded a higher favorability rating than did Schaefer in the poll.

In the Senate race, Mikulski was the choice of 43 percent of voters, followed by Hughes with 21 percent, Barnes with 13 percent and Hutchinson with 6 percent. Mikulski's favorability rating also was high, with 59 percent having a favorable opinion of her and 9 percent unfavorable.

The Post survey included Democrats who said they have at least a 50-50 likelihood of voting in the September primary. The sampling contains a margin of error of 4 percentage points.

Among a smaller sample of 327 respondents who were considered "likely" voters because of past voting patterns and their interest in politics, Sachs narrowed the gap slightly, and Mikulski expanded her lead. Among those likely Democratic voters, Schaefer led his opponent in the governor's race by a 5-to-2 margin, and Mikulski outpolled Hughes by more than 5 to 2. Barnes and Hutchinson moved up a few percentage points in the smaller sample, which had a margin of error of 6 percentage points.

Although among potential voters Hughes leads Barnes by a significant margin, voter attitudes on Maryland's savings and loan crisis pointed to continued difficulties for the two-term governor.

The Post poll surveyed 1,414 Maryland residents on the savings and loan issue. A vast majority said they do not view the thrift crisis as resolved, and half said they believe that the problem is "very serious." Thirty-eight percent rated it as "serious."

In addition, 51 percent disapprove of the way Hughes has handled the crisis, and 21 percent said they had no opinion. Only 28 percent approved of his efforts to cope with the thrift crisis, indicating that the governor has been tarnished by the issue and will have to intensify his recent efforts to explain his handling of it.

Overall, however, more of those surveyed blame the Maryland General Assembly than blame Hughes for the thrift crisis. Forty percent said they assign a "great deal" of the blame to the 188-member legislature, while Hughes, by comparison, is given a "great deal" of blame by 33 percent of respondents.

One bright spot for Hughes is that despite public displeasure with his performance in the crisis, few Democrats absolutely rule out voting for him. The governor, in fact, remains the preferred second choice of many Democrats who were surveyed.

Hughes, who won his second race for governor four years ago by capturing 62 percent of the vote, suffered from a higher unfavorable rating than any Democrat running statewide this year. Though the governor is viewed favorably by 44 percent of potential Democratic voters, he is viewed unfavorably by 34 percent, an unfavorable rating about four times as high as those of his three opponents.

The survey found that Mikulski is not hurt and may be helped by her status as the only woman in the Senate race. The five-term Baltimorean, who has been closely associated with feminist issues during her political career, is favored by 46 percent of the women surveyed. Eleven percent of the women said they are more inclined to vote for Mikulski because she is a woman. Two percent of women and 3 percent of men said they were less inclined to vote for her because of her sex.

Mikulski's strength among women could be a significant advantage because women are expected to make up about 55 percent of the voters in the two Democratic primary contests in the fall.

Geography also seems to favor Mikulski and penalize her opponents in the Senate race.

Although Mikulski runs third in the Washington suburbs to Barnes and Hughes, she overpowers her opponents in Baltimore and the Baltimore suburbs, leading her nearest challenger by better than 4 to 1 in those two regions. During the 1982 Democratic primary, Baltimore and Baltimore County contributed 46 percent of the statewide voter turnout, compared with 22 percent from Montgomery and Prince George's counties.

Mikulski's strength is greatest among older voters, among low-income voters, and among the one-quarter of those surveyed who indicate that they are liberal. She also leads, though not by as much, among moderate and conservative Democrats. In addition, 66 percent of her backers identify themselves as "strong supporters," compared with 58 percent of Barnes' supporters and 32 percent of Hutchinson's followers.

Another indicator of Mikulski's strength is that she would draw significant support from those who support Hughes or Barnes if either of them abandoned the race. Asked who their second choices were in the Senate race, 36 percent of Barnes' supporters said Mikulski, while 30 percent chose Hughes. Twenty-five percent of Hughes' supporters said their second choice was Mikulski, and 30 percent said Barnes.

Barnes, who has proved over the years to be a potent vote-getter in his home base of Montgomery County, heads the Senate field in the Washington suburbs. But he is virtually unknown elsewhere in the state. He is the favored candidate of only 2 percent of Democrats in Baltimore City, and of only 5 percent in the Baltimore suburbs.

"Mike's number one problem is that he is not well known," conceded John T. Willis, Barnes' campaign manager. But he added that their data suggest that many voters could switch to Barnes when they learn more about him.

Hutchinson, who is completing his second term as Baltimore County executive, suffers low ratings even in his home district. In the Baltimore suburbs, where he makes his strongest showing, only 13 percent of Democrats support him, putting him 48 percentage points behind Mikulski in his home base. Sixty-four percent of Democrats statewide said they do not know enough about Hutchinson to rate him, and he is a virtual nonentity in the Washington area.

The Post poll confirms earlier findings that the 64-year-old Schaefer is a political figure of almost overwhelming proportions.

Sixty-eight percent of those who indicated they will vote for the Baltimore mayor say they "strongly support" him. In comparison, just 36 percent of Sachs partisans say they "strongly support" the two-term attorney general.

Not surprisingly, Schaefer runs extremely well in the city where he has served in public office for 30 years. Seventy percent of Baltimore City Democrats prefer Schaefer, compared with 20 percent for Sachs. Schaefer leads in the Washington suburbs 36 to 17 percent, although 47 percent are undecided.