Reflecting "better-than-expected" results in the May-July months, Marriot Corp. reported yesterday a 39 percent increase in profits for the fiscal year ended July 28.

Record earnings of $46.1 million ($1.26 a share) were substantially higher than the $35.5 million (97 cents) earned in the previous year because of business expansion and higher profits margins, according to company president J.W. Marriott Jr.

Sales of the Bethesda-based hotel, restaurant, food service and amusement park firm rose 15 percent to a record $1.18 billion.

Operating results for the full year were buoyed by record quarterly profits of $15.2 million (41 cents a share) in the final three months of the fiscal year, up 37 percent from $11.1 million (30 cents) last summer on a 16 percent sales gain to $319 million.

Marriott said a strong growth in hotel business and an upswing in profits at the firm's two amusement parks (particularly the one at Gurnee. Ill., near Chicago) helped bring fourth-quarter profits to a level 18 percent higher than in any previous three-months period in the company's 51-year history.

Business at the Marriott parks in Illinois and at San Jose, Calif., had been sluggish earlier in the season. The company still is considering whether to build a third park between Washington and Baltimore.

In a prepared statement, Marriott said he is "particularly proud" of the 1978 profit improvement in the face of "substantial obstacles working against us: Food costs spiraled 12 percent the past 12 months . . . . the federal minimum wage jumped an inflationary 15 percent . . . . winter weather closed airports and kept customers home . . . . energy costs continued to rise."

Hotel rates were increased and some food prices also were boosted to absorb rising expenses. Marriiott hotel profits rose 29 percent and sales jumped 20 percent in the year as the number of rooms under company management increased 16 percent with the addition of four hotels. Restaurant operations posted a 21 percent increase in profits while contract food service profits rose 8 percent.

The company is changing its fiscal year to a period ending in February and will hold its annual meeting on Nov. 21 at the Shoreham Americana Hotel in Washington.

W. Bell & Co., a Rockville catalogue showroom merchandiser, has reported record sales and profits in the fiscal year ending June 24.

Earnings sored 123 percent to $1.56 million ($1.64 a share) compared with $701,100 (73 cents) in the previuos year as sales jumped 31 percent to $58 million.

For the fourth quarter alone, Bell earned $338,900 (36 cents a share) on sales of $13.8 million compared with profits in the same period last year of $160,200 (27 cents) on sales of $10.3 million.

Bell, which sells good from 10 showrooms in Maryland, Virginia, D.C., Georgia and Texas, is planning to open two new units in the near future.

An 18,600-square-foot showroom will be opened at Springfield Mall this month and a 33,500-square-foot unit is scheduled to open at Tysons Corner in November. A Bell showroom in downtown Baltimore will be relocated to South Charles Street this month.

Fair Lanes Inc., a Maryland bowling center firm, reported yesterday earnings of $4.2 million ($1.05 a share) for the year ended June 30 compared with $3.5 million (83 cents) in the prior fiscal year. Revenues increased to $47 million from $42 million.

Fourth-quarter profits were $668,75 (17 cents) vs. $486,803 (12 cents) as revenues rose to $11 million from $10 million.

Vega Precision Laboratories reported a 9 percent increase in profits for the six months ended June 30. Earnings were 65 cents a share compared with 60 cents as sales rose 65 percent to $6.6 million.

The Vienna manufacturer of radar tracing, command and control systems attributed recent gains to development of new products. Vega's unbilled backlog of business was estimated at $8 million.

Microdyne Corp., a Rockville manufacturer of satellite television receiving equipment, reported sharp increases in sales and profitability during the nine-month period ended July 30.

Net income rose to $566,140 (48 cents a share) compared with $131,950 (12 cents) in the 1977 period, an increase of 329 percent. Sales rose 92 percent to $5 million.