About 650 Prince George's County Democrats paid $100 each for tickets to a fund-raising event last night to launch the campaigns of Maryland Senate President Sten Hoyer for governor and Winfield M. Kelly Jr. for a second term as county executive.

After deducting $15 per person to pay the Sheraton Lanham for food, the two Prince George's Democrats stood to split more than $55,000 for their election efforts.

Facing stiff competition from college basketball tournaments on television and St. Patrick's Day festivities at various locations, the affair's organizers nevetheless predicted that the number of contributors last night might exceed 700.

Lance Billingsley, Prince George's Democratic Party chairman, had given County Council members two tickets each - one free, the other to sell. At least one member of the all-Democratic Council, Francis B. Francois, is considering opposing Kelly next year. He said yesterday he wasn't asked to sell any tickets to raise funds for his potential opponent, but he was using his complimentary ticket for himself.

The fund-raising affair at the high-rise hotel by the Capital Beltway, where virtually all local Democratic functions are held, bespoke a powerful political alliance between Hoyer, 39, and County Executive Kelly, 41, that has party leaders around the state somewhat in awe.

The Prince George's General Assembly delegation is already considered a powerhouse in Annapolis. With last night's scheduled event, there existed at least the possibility of a governor from Prince George's for the first time since Oden Bowie vacated the state executive mansion in 1872.

Over recent months, Hoyer has been meeting with small groups of Democrats throughout the state to win early support in an increasingly crowded field of contenders.

Hoyer is an admittedly ambitious politician and a deft one. When California Gov. Jerry Brown campaigned for the Presidential nomination in Maryland last year, Hoyer is said to have remarked, "If that guy can be President, so can I." He has declined to describe his political philosophy, saying he prefers instead an "issue by issue" approach.

In a recent interview, Hoyer said he is against capital punishment and for mandatory sentences. "I supported most civil rights measures, open housing. I'm against busing," he asserted. Such descriptive terms as liberal and conservative are "irrelevant in this day and age," he said.

The alliance, between Kelly and Hoyer developed after the county executive dropped his own gubernatorial ambitions, at least for 1978.

"Steny's been around (politically) a lot longer than I have," Kelly said in an interview a few months ago. "We've talked about it, and I've chosen, based on everything, to support Steny."

Describing himself as "sort of an independent maverick," Kelly said he had told Hoyer "he (ought to) stay as president of the Senate. It gives (Prince George's County) a lot of prestige, and he's a damn good representative of the county. He makes us look good and I like that . . .

"But I recognize the fact that he wants to do what he wants, and I'm willing to support him, and I don't have any aspirations," Kelly said. "I have so many things I've started here. I wan to finish some of them . . . It will be nice to have a governor from Prince George's County."