On a steamy afternoon with the temperature hovering at 98 degrees, Mike Boddicker shut out the Texas Rangers on four hits today, completing the hottest July in Baltimore Orioles' history.

The 6-0 victory, which included home runs by Eddie Murray and Gary Roenicke, was the Orioles' fifth straight, and helped them take a one-game lead in the American League East over Detroit, which split a doubleheader with Kansas City. The Orioles finished 19-7 (.731) for the month; in the past 10 years, their .601 winning percentage in July is the best in the major leagues.

"Our best July ever, is that right?" said surprised Manager Joe Altobelli, luxuriating with a postgame cigar. "We've come from behind, had excellent pitching, like today, and had timely hitting. That's what did it."

One of the people responsible for this July was sipping a beer, recounting his third shutout of the season--all at home--and second this month.

"I changed speeds on my slider, curves and changeups," said Boddicker (7-5), 5-0 with a 1.69 ERA at Memorial Stadium. "I kept thinking I was going to get tired, but I never did."

Ray Miller, pitching coach, looked over at the 25-year-old rookie and said: "Today he was as calm as I've ever seen him. He doesn't get nervous, but he gets himself too psyched up. But today he was relaxed, he was talking between innings."

Before 23,174, the Orioles essentially won this game in the first inning.

John Shelby led off with a single to center, took third on Murray's checked-swing looper to right then scored when Roenicke singled to center.

Ken Singleton, hitting just .243 right-handed, hit Frank Tanana's high and tight fast ball past diving shortstop Wayne Tolleson, scoring Murray to give the Orioles a 2-0 lead.

After giving up a single to Buddy Bell in the first, Boddicker retired the next 13 batters before walking Jim Sundberg. In all, Boddicker threw 102 pitches (41 fast balls, the rest a mixture of fork balls, change-ups and curves), facing 30 batters, three over the minimum. "The reason the hitters were swinging so funny was because of that fork ball," said Miller.

Murray drove a high 3-2 fast ball from Tanana over the left field fence in the third for his 21st homer of the season and a 3-0 lead. "He tried to put it up and in," said Murray. "I don't think that's what he wanted to do. I saw the ball all the way."

The Rangers, losers of six straight and 19 of 24 since the All-Star Game, had the kind of sixth inning that typically befalls a losing team. Bell, the Gold Glove winner at third the last four years, made two errors in the inning, setting up the next two runs.

First, Bell misplayed a routine grounder by Roenicke. After Tanana got two quick outs, Bell threw wildly to first on a grounder by Rich Dauer.

The new pitcher, Dave Schmidt, threw a wild pitch, scoring Roenicke. Finally, Rick Dempsey, hitting .229, hit a double against the fence in left center.

Roenicke, seven for 17 in his last six games, hit a 1-2 slider by Odell Jones in the eighth inning for the Orioles' final run. "He got it up and it didn't break much," said Roenicke. "He threw it 90 mph. It felt good because it's been a struggling month for me."

Boddicker, unlike Roenicke, did not struggle in July. In fact, Bod-dicker, second-year pitcher Storm Davis and rookie Allan Ramirez have kept the Orioles at or near the top of the AL East almost the whole month, particularly striking because three of the Orioles' best pitchers--Jim Palmer, Tippy Martinez and Mike Flanagan--have been on the disabled list most of July.

"Those kids are the reason why we've done so well," said Altobelli. "We've never had a worst of anything because of them."

It's the slightly built Boddicker who has been the pleasant surprise of the season. Before the season, Miller had designated him No. 9 on the staff. But a severe ankle sprain prevented Boddicker from opening with the team.

After Palmer went on the disabled list May 5, Boddicker was recalled from Rochester and subsequently pitched a 5-0, five-hit shutout against Chicago May 17. "That's been my best game," he said.

"He's especially tough for day games here," Miller said, "because he changes speeds so well."