Former Republican Congressman Lawrence J. Hogan, one of the few successful GOP politicians in Prince George's County over the last decade, will tomorrow announce his candidacy for county executive, according to authoritative sources.

The entrance of the 49-year-old Hogan into the race for the county's top office has been anticipated for several weeks. He is expected to make it official at a press conference scheduled at the Capital Plaza shopping center tomorrow morning.

Leaders of the larfely powerless county Republican Party view Hogan as the best, and perhaps only, hope to unseat County Executive Winfield M. Kelly Jr., the incumbent Democrat.Kelly, who faces no serious opposition in the Democratic primary, has said that he has begun a re-election campaign based on the expectation that Hogan would be his opponent.

"Larry's a very tough campalgner," Kelly said in an interview last week. "Our polls show that the people know him, and a lot of them like him. It's going to be a helluva race, but we've prepared for it. Everything we've done has been to get ready for something like this."

Hogan was not available for comment over the weekend. Sources close to him said that Hogan did not make up his mind to run until last week, when he determined that he would have sufficient money and support to challenge the popular incumbent.

Before he meets Kelly in the November election, however, Hogan must first turn back the challenge of Oxon Hill developer Martin Aragona in the Republican primary. Aragona announced for the Republican nomination three months ago and already had begun a television advertising campaign. The party regulars regard him having little countywide support.

"Larry getting into this is the most exciting thing I've heard around here in a long time," said Melissa Martin, the county Republican, chairman. "This could mark a rejuvenation of the party." Since Martin became chairman in 1974 every elected office in the county has belonged to the Democrats.

Hogan began his career in county politics in 1966 when he defeated incumbent Democratic Rep. Hervey G. Machen for the 5th District congressional seat.During his eight-year tensure in the House, Hogan was known as a staunch defender of former Pres. Richard Nixon, until in 1974, as a member of the House Judiciary Committee, he voted for Nixon's impeachment.

The vote against Nixon came at a time when Hogan was preparing a campaign for the Republican nomination for governor in Maryland. He lost that race to Louise Gore, who eventually was defeated by now suspended Gov. Marvin Mandel.

Since his 1974 defeat, which took both him and Mandel by surprise, Hogan has served as the Republican National Committeeman from Maryland. He recently resigned under pressure from a post as executive director of Associated Builders and Contractors Inc., after leaders of the national organization charged that Hogan was using his post for political purposes.