About 600 Maryland Republicans plunked down $100 each tonight to listen to members of their national party, most notably Senate Majority Leader Howard Baker (R-Tenn.) tell them that support for President Reagan on the national level would result in success on the local level in November.

"Do not forget," said Baker, the keynote speaker at the Republican "victory dinner" at the Hyatt Regency Hotel, "that I ran against Ronald Reagan in 1980. But I have worked with him as president and I support what he is trying to do and what he has already done. Whatever Democrats say, I think all would agree that Ronald Reagan is as dedicated and resolute a president as we have ever had and I think everyone in this room would agree that we have the opportunity and the chance to succeed in elections this November."

Baker was brimming with enthusiasm after flying in by helicopter from a late Senate session along with Maryland Sen. Charles McC. Mathias. He called Republican gubernatorial candidate Robert A. Pascal "a man who deserves to be governor and a man who will win with an overwhelming majority." He called Mathias "one of the greatest senators of all time."

Baker also predicted that Republicans will increase their majority in the Senate this fall by two to four seats. On the local level, party chairman Allan C. Levey predicted a gain of 10 to 15 seats in the state legislature.

This was a night to make money--GOP officials hoped to gross $60,000--discuss the campaigns and gossip. Most of the gossip centered on the two questions that have remained unanswered for months: Whom will Pascal choose as his candidate for lieutenant governor and will former Sen. J. Glenn Beall Jr. get into the Senate race?

"Haven't decided yet," said Pascal.

"Haven't decided yet," said Beall.

With 13 days left before the filing deadline, those answers brought little relief to Republicans. Most of the speculation for lieutenant governor now centers on former representative Newton I. Steers of Montgomery County. Pascal has not yet spoken to Steers but has sent out feelers through mutual friends.

The other name being tossed around was that of Dallas Merrell, who is currently running against Prince George's County Executive Lawrence J. Hogan for the Republican nomination for the Senate.

"Haven't heard a thing," Merrell said during the host's cocktail party, which required a minimum $1,000 contribution for entry. "I'm running for the Senate."

Beall has remained a definite maybe for several months. Tonight, several of his business friends said Beall was planning to make a final round of phone calls over the next 48 hours and planned to talk to Mathias before making up his mind.

Republican notables were here in force--Pascal, Hogan, Beall, Merrell. Also former gubernatorial candidate Louise Gore; former representative Robert A. Bauman, and Delaware Gov. Pierre S. duPont IV, who was the other speaker on tonight's program.

Although there were a number of empty seats the Republican mood was generally upbeat. "The key for Republicans in this state is getting the exposure that they need to let people know what they are about," duPont said. "Money is the key to that."