Marian L. Greenblatt, the controversial conservative member of the Montgomery County Board of Education, is expected to announce next month that she will run for U.S. Congress, sources in the county Republican Party said this week.

Party sources said she is leaning heavily toward a congressional race against the popular Democratic incumbent, Rep. Michael D. Barnes, and has virtually ruled out running for county council or county executive, the two other offices she was known to be considering. One party source who had talked to Greenblatt said she is "95 percent certain" she will run for Congress.

Greenblatt, a former Democrat who switched parties last July, said yesterday that she has met with party officials but has not made a final decision on which race to enter.

"I'm going to be making a decision one way or the other in the next month," Greenblatt said. "There are several options I'm looking at."

Several party leaders have urged Greenblatt to begin publicizing her candidacy. But, they said, before announcing she will attempt to raise campaign money to be sure a congressional race is possible.

Several Republican Party officials said Greenblatt is the best candidate the party can field, as well as one who is willing to run against Barnes.

"Who else have we got?" asked one Republican who declined to be named.

Paul Clark, the county Republican Party chairman, said Greenblatt "has good name recognition and, if she were to run, would scare Mike Barnes more than any other Republican in that district."

Still, Republican sources conceded that Barnes is tough to beat and that only a revitalized economy would give a Republican candidate a chance.

The county has twice as many Democratic voters as Republicans, and Barnes, according to polls, is viewed favorably by most. As a congressional candidate, Republican strategists said Greenblatt would need to overcome her negative image among some voters, the result of her outspoken stands on racial issues.

Some Republican leaders said they hope Greenblatt will run for Congress to avoid bitter primary campaigns in the county races.

One moderate Republican, Del. Luiz Simmons, already has decided to run for county executive. Sources said that to emphasize his moderate credentials, he would portray Greenblatt as a far-right conservative if she challenged him in a primary.

County Republican leaders hope to agree before the primary election on a slate attached to the likely Republican gubernatorial candidate, Anne Arundel County Executive Robert Pascal.

Greenblatt should avoid a local race, some Republicans believe, because of the negative image she received during last fall's school closings. They say her presence could hurt Republican candidates running for county council, and that if her stormy relations with minority groups become an issue, she could hurt the party's standing overall.

By running for Congress, Republican Party strategists said, Greenblatt could portray herself as a Reagan-style Republican and could speak out on matters such as the economy and the security of Israel, both of which concern county voters. According to party sources, she could attack Barnes as a big-spender who is more liberal than the average voter.

Greenblatt has spent five years on the school board, leading the board's dramatic shift to conservative educational and racial integration policies.

According to sources close to her, Greenblatt believes she could win a county council election, but isn't interested because the council is dominated by liberals, as the school board was when she first was elected. She also is leaning against the county executive race, sources said, because of Simmons and because she would not enjoy working with a liberal council.

Greenblatt's term on the school board expires in 1984. She would not lose her seat if she ran and lost in a partisan election later this year.