Maryland Attorney General Stephen H. Sachs, surging in popularity among black voters, has cut in half the gap in the race for the Democratic nomination for governor but still trails Baltimore Mayor William Donald Schaefer by a margin of nearly 2 to 1, according to a new Washington Post poll.

Schaefer is preferred by 52 percent and Sachs by 30 percent, with 17 percent undecided, in the most recent Post poll, conducted June 21-25 among 752 potential voters in the Sept. 9 Democratic primary.

In a Post poll taken in March, 59 percent favored Schaefer, compared with 19 percent for Sachs and 22 percent undecided or supporting other candidates.

In the race for the Democratic nomination for the Senate seat being vacated by retiring Sen. Charles McC. Mathias (R-Md.), Rep. Barbara A. Mikulski of Baltimore has enlarged the solid lead she established early in the campaign, the new Post poll found.

Mikulski is supported by 48 percent of those interviewed recently, while 20 percent choose Rep. Michael D. Barnes of Montgomery County and 19 percent favor Gov. Harry Hughes. Twelve percent say they are undecided.

In the March poll, 43 percent backed Mikulski, compared with 21 percent for Hughes, 13 percent for Barnes and 6 percent for Baltimore County Executive Donald P. Hutchinson, who has since dropped out. Seventeen percent of the respondents said they were undecided.

Mikulski was "gratified" by the poll results, spokesman James Abbott said. But he urged caution, saying, "A lot of Marylanders still haven't focused on this race and probably won't until the last two weeks, so we're going to go full steam ahead."

Barnes, campaigning in the Baltimore neighborhood of front-runner Mikulski, took a more optimistic view of the findings, noting that he had "gone up the most of any candidate," while Hughes "has gone down despite spending a lot of money."

The latest poll results were discouraging news to Hughes' campaign advisers, who had hoped the governor had "stopped the bleeding," as campaign manager John W. Eddinger put it.

In the contest for the gubernatorial nomination, Sachs' choice of a running mate seemed to be the primary factor that allowed his underdog campaign to begin eroding the political strength that Schaefer has gained over 15 years as mayor of a populous city with a well-publicized renaissance.

This month, Sachs surprised political observers when he selected Rep. Parren J. Mitchell (D-Md.) of Baltimore, a popular black politician, as his choice for lieutenant governor. That decision appears to have helped him significantly among black voters, who compose 21 percent of the state's voting-age population.

Sachs is the choice of 46 percent of the blacks surveyed, compared with 36 percent for Schaefer, with the rest undecided. In March, blacks preferred Schaefer 59 percent to 20 percent; the remainder were undecided.

But Sachs gained only 3 percentage points among whites in the most recent Post poll. He closed the overall gap from 40 points to 22, but Schaefer is still the choice of more than half of the poll's respondents.

Sachs supporters hailed the poll results as a sign that the attorney general's campaign is catching on among voters who had not been paying attention to it far in advance of the Sept. 9 primary. "With Parren on board, there's a spark that's caught fire in this campaign," said Sachs' campaign manager, Blair Lee IV.

They said they were relieved that Mitchell's candidacy apparently has not provoked a racially tinged backlash among white voters.

Schaefer said that he believes that the Sachs spurt shows that Mitchell has aided a campaign that was "languishing." He added that "our people were getting a little complacent" because of the comfortable lead his campaign has enjoyed.

Schaefer's choice of state Senate President Melvin A. Steinberg (D-Baltimore County) as his running mate has had no appreciable effect on the strength of Schaefer's candidacy, the poll showed.

Twenty-five percent of all those polled and 46 percent of those identifying themselves as Sachs supporters say that they are more likely to vote for Sachs because of Mitchell's presence on the ticket, and 49 percent are able to name Mitchell as the black candidate for lieutenant governor.

Only 13 percent of all those polled and 18 percent of voters who identified themselves as Schaefer supporters say that Steinberg's presence as Schaefer's running mate would make them more likely to vote for the mayor.

Another apparent side effect of Sachs' growing strength among blacks following his pairing with Mitchell was the fact that he became a slight favorite among all voters in Prince George's and Montgomery counties, which produce as much as 30 percent of the statewide Democratic vote.

In the area of potential campaign issues, Schaefer consistently outpolls Sachs when respondents were asked which candidate would best handle matters ranging from the state's savings and loan crisis to the Chesapeake Bay cleanup.

Respondents generally seem not to be focusing on the contests, however. Half those surveyed say they had not been following news about Maryland politics closely or at all.

In addition to the 752 voters who say they have at least a 50 percent likelihood of voting in the Democratic primary, The Post surveyed 268 registered Republicans who are considered potential voters in their party's primary. The margin of error is 4 percent among Democrats and 6 percent among the smaller Republican sample.

In the GOP Senate race, for example, 73 percent of potential Republican voters say they are undecided. Of those who expressed a preference, 11 percent support former White House aide Linda Chavez, 9 percent support former Baltimore businessman Richard Sullivan and 4 percent back Montgomery County lawyer George Haley.

Del. Thomas J. Mooney of Prince George's County is running unopposed for the GOP nomination for governor.

The future of the Chesapeake Bay became a particularly thorny issue for Schaefer in April when Sachs and some environmentalists criticized him for suggesting that the state rockfish ban be lifted and shore-development restrictions relaxed within two years. But 47 percent of those polled say that Schaefer would do a better job of reducing pollution of the bay than Sachs, who got 19 percent.

The results indicate that although voters say they would support Sachs' proposal to increase the state sales tax from 5 to 6 cents on the dollar to improve public education, 60 percent are unsure which candidate made the proposal.

Sachs has dubbed the proposal "a penny for education," and he uses it as the cornerstone of his campaign, wearing a copper 1-cent coin in his lapel when he campaigns. During the weeks after the proposal was announced, the Sachs campaign spent about $60,000 on radio and television advertising to promote the idea.

Fifty-nine percent of the voters say they favor the idea, even though tax increases are not normally popular with voters.

Schaefer is still the better-known candidate, and 71 percent of those polled say that they hold a "favorable" opinion of him. Fifty-two percent say the same of Sachs.

The Senate race offers fewer dramatic shifts.

Barnes picks up 7 percentage points, some of which came in the Baltimore area (the city, Baltimore County and parts of Howard and Anne Arundel counties), which can account for as much as 42 percent of the vote in statewide Democratic primaries.

The standing of Hughes, a two-term governor with the broadest name recognition of any of the Senate candidates, remains static despite the withdrawal from the race this month of Hutchinson, who vied with him for the backing of those seeking a "moderate" alternative to Mikulski or Barnes.

He shows no gain despite an expensive month-long television advertising campaign aimed at blunting criticism of his handling of the yearlong savings and loan crisis. Hughes strategists blamed the crisis for his current rocky political fortunes.

Although the respondents appear to have softened earlier criticisms of the governor's handling of the crisis -- 39 percent of those now surveyed say they approve of his efforts, compared with 28 percent in March -- he remains the Senate candidate with the highest negative image among voters.

In the Washington area, where Barnes is strongest, with support from 37 percent of voters, Mikulski is supported by 29 percent of those polled, an 8 percentage point increase since March. Hughes falls to 16 percent, 10 points below where he was in March.

Hughes campaign manager Eddinger acknowledged in an interview what Hughes advisers had said privately for weeks -- that they consider this month's poll results crucial to their fund-raising efforts, where Hughes lags behind Mikulski and Barnes despite what he considers his broader appeal to the moderate business community.

"It's very puzzling. It's a pretty big deficit to overcome, I'll be candid," said Eddinger.

"Harry's been around for eight years. They the voters know him. I guess they feel the whole S&L situation really has him stuck, and I guess they feel he hasn't handled it correctly. If that's the case, I guess we've got a problem."

Hughes, who formally filed his statement of candidacy last week, "has no intention of pulling out," said Eddinger.

Barnes, who has also spent about $100,000 on television ads in recent months, about the same as Hughes, showed slight gains in all parts of the state.

In Baltimore, where he was the choice of only 2 percent of those surveyed in March, he is favored by 11 percent of potential voters in June. In the Baltimore suburbs, where he was the choice of only 5 percent of the voters in March, he is now favored by 14 percent.

Barnes has made a special effort to woo black voters, and in the most recent poll, he shows gains among them. But those gains are no larger than his gains among whites. Nine percent of black Democrats surveyed in March selected Barnes, compared with 15 percent in June. That compares with 15 percent of whites in March and 22 percent in June.

Mikulski also made strong gains among black voters, however, consistent with her lead throughout the state and with virtually every group surveyed.

Although she has yet to rely heavily on paid advertising -- she bought about $10,000 in radio time last month -- she has held onto her lead in Baltimore and its suburbs, where 64 and 60 percent of voters, respectively, support her.

She continues to enjoy strong support across ideological lines as well: Voters who identify themselves as conservative select her as their choice only slightly less frequently than do moderates and liberals.

Mikulski's campaign themes, emphasizing her strong personality, record of advocacy and familiarity with common concerns, appear to be striking a responsive chord with voters.

On the question of understanding national needs and problems, which Barnes has emphasized as one of his strengths, voters still prefer Mikulski. And on the question of which candidate best understands Maryland's needs, a theme that is the cornerstone of Hughes' campaign, 40 percent of those polled select Mikulski, and only 25 percent choose Hughes.

Staff writers Sandra Sugawara and Tom Kenworthy contributed to this report.