A Montgomery County group that was formed to support black political candidates and their allies flexed its muscles for the first time this week when it endorsed state Sen. Sidney Kramer's bid to become county executive.

In endorsing Kramer, the Citizens for Equal Representation in Government (CERG) spurned an overture by David L. Scull, Kramer's chief rival.

Kramer said he was delighted by the endorsement, a largely symbolic victory that came after a dramatic hour-long voting session at the Wheaton Regional Library Monday night.

CERG members endorsed Kramer and several other candidates on a 39-to-13 vote, barely the required two-thirds majority.

A spokeswoman for Scull said he remains confident "the black community at large" will support him over Kramer in the Democratic Party primary in Sept. 9. Democrats Agree on Ticket

Prince George's County Democrats have finally reached a tentative agreement on who will be endorsed officially for the Sept. 9 primary.

The county's eight state senators and County Executive Parris N. Glendening settled last week on the names and faces to appear on the "ticket," a brochure listing the candidates endorsed by the county's dominant Democratic faction.

The ticket is the subject of anxiety, lobbying and jockeying in the months (and years) before an election, for it is believed to hold the key to electorial success in Prince George's, especially in less-visible local races. But the endorsement is also coveted by statewide candidates because it is made by the county's largest political organization.

Always a source of controversy, negotiations over the ticket were complicated this year by the deep divisions over the gubernatorial and state's attorney races and, to a lesser extent, the U.S. Senate race.

The solution? To form "topless tickets" in which local candidates would endorse each other but leave off endorsements of the top, statewide races.

The final decisions, according to Glendening, are:

* In six out of eight legislative districts -- all those except the Clinton-based 27th of Sen. Thomas V. Mike Miller Jr. and New Carrollton-based 22nd of Sen. Thomas P. O'Reilly -- the tickets will be topless as to the governor's race.

In the 27th and 22nd districts there are a number of party regulars who support Baltimore Mayor William Donald Schaefer's candidacy, so his name will appear on the ticket. In the others, officials are divided between Schaefer and Attorney General Stephen H. Sachs. If they choose, they can print separate brochures listing their respective endorsements in that race.

* In the state's attorney's race, Democrats in six out of eight legislative districts have agreed to support either challenger Alex Williams or no one. In the other two, again the 22nd and 27th, the literature will endorse incumbent Arthur (Bud) Marshall.

* The Senate race remains up in the air, so officials decided to go ahead with an initial printing without any endorsement until they can make up their minds. 8th District Entry

Phillip N. Buford, a Republican from Bethesda, has entered the race for his party's nomination to the 8th District congressional seat.

Buford, who ran unsuccessfully for the seat in 1982, said he was challenging fellow GOP members Constance A. Morella and William S. Shepard because he can "best represent" Montgomery County in Congress.

Incumbent Rep. Michael D. Barnes, a Democrat, is leaving Congress to run for the U.S. Senate.