The statewide poll found Mr. Sarbanes leading the Republican by 56 percent to 33 percent, with 11 percent of voters still undecided.
Political analysts saw the poll results as gloomy for Mr. Brock, a former Tennessee senator who is trying to upset the 18-year incumbent Democrat.
"Sarbanes is starting to run away with this," said Del Ali, vice president of Mason-Dixon Political Media Research Inc. of Columbia, which conducted the poll for The Sun and other news organizations.
Mr. Brock emphasized the positive, pointing out that he has risen 10 percentage points since the last poll taken in late August. That survey showed Mr. Brock with just 23 percent of the vote, compared with Mr. Sarbanes' 58 percent.
"I'm delighted," Mr. Brock said of yesterday's results. "I think we've come further and faster than I expected."
He also said he believes that the number of undecided voters is much higher than the poll indicated and that there are many he can still woo before the Nov. 8 election.
For the poll, 829 registered voters, selected at random, were interviewed by telephone Wednesday through Friday of last week. All said they vote regularly in state elections. The margin of error was plus or minus 3.5 percentage points.
It showed Mr. Brock with the lead in the state's traditionally more conservative areas, the Eastern Shore and Western and Southern Maryland. But Mr. Sarbanes led Mr. Brock in all of the state's major population centers, including Baltimore City and Montgomery and Prince George's counties.
In hopes of narrowing Mr. Sarbanes' lead, Mr. Brock is going after the senator for the first time in the campaign with a television advertisement that portrays Mr. Sarbanes as a tax-raiser.
The ad, which will begin airing today on both Baltimore and Washington television stations, claims Mr. Sarbanes cast the deciding vote in favor of the 1993 tax increase President Clinton proposed to help reduce the deficit.
In fact, while Mr. Sarbanes did support the measure, he did not cast the deciding vote. Vice President Al Gore broke the 50-50 tie in the Senate to pass the bill. Mr. Gore is the son of Al Gore Sr., the former Tennessee senator whom Mr. Brock defeated for his seat in 1970.
"He thinks he's running against another Gore," said Sarbanes campaign manager Michael Davis, who described the ad as "a desperate act."
The ad also says Mr. Brock wants to cut taxes. It fails to mention, however, that he proposed a $10 billion-a-year tax increase on gasoline in 1988 while testifying before the National Economic Commission in Washington.
Mr. Brock also worked on a 1992 report by the Center for Strategic and International Studies that proposed a plan that "includes increases in taxes . . . producing $376 billion for deficit reduction."
Mr. Brock said yesterday that the organization did not really propose a tax increase. Instead, it was a restructuring of the tax system that would create more jobs that, in turn, would increase revenues, he said. He added that the participants in the report were not bound by any of its specifics.
Interviews with more than a dozen Republican campaign officials, legislators and candidates in the past week revealed a mixed assessment of Mr. Brock's election chances.
On the record, some GOP officials say he can win if he focuses on a single message, draws a clear contrast with the incumbent and capitalizes on voter discontent.
"I think Brock has a real chance of pulling an extraordinary upset," said 1st District Rep. Wayne T. Gilchrest.
But others in the party speaking on condition of anonymity questioned whether the race can be won.