The Portland Trail Blazers yesterday obtained the first choice in today's National Basketball Association draft from the Indiana Pacers. A Portland official said the 1977 NBA champs would select either Indiana State forward Larry Bird or Minnesota forward-center Mychal Thompson.

After a proposed deal with the Philadelphia 76ers for forward George McGinnis fell through, the Pacers landed playmaking guard John Davis, a Portland starter and two-year veteran, and the third pick, one of Portland's three first-round choices, in today's draft.

Portland Vice President Stu Inman said the Blazers would work until the noon start of the draft to convince Bird to pass up his senior year of eligibility and sign immediately. Inman said Bird told him he is leaning toward staying in school. If the 6-foot-8 forward does not change his mind, Portland will take Thompson.

The Blazers would then hope that Bird still is available for their second choice in the first round, the No. 7 pick overall. Portland, which had the league's best won-lost record this season, obtained both top choices through previous trades for Moses Malone and Wally Walker.

The Portland-Indiana transaction topped a heavy day of jockeying for position in the draft.

As previously reported, the New York Knicks and New Jersey Nets switched first-round drafting positions for the next two years as partial settlement of the Nets' $3.2 million indemnity payment to the Knicks. The Knicks now draft fourth, the Nets 13th and New Jersey also ends up with 10-year veteran Phil Jackson.

Portland also dealt its own first-round choice, the 22nd and last pick of the round, to Golden State for the Warriors' first-round pick in either 1980 or 1981. The Warriors can decide which year.

The NBA champion Bullets will have two first-round picks: their own, the 14th, and Denver's, the 18th, as a result of the Bo Ellis trade.

It is most likely that Portland will end up with Thompson. Bird's college coach, Bob King, said yesterday, "He'll be playing for us, but it wouldn't surprise me if Bird signed a contract with the Blazers next spring."

Bird is eligible for the draft because his high-school class graduated four years ago.

If Bird does not reconsider and Portland takes Thompson, Kansas City, drafting second, would take North Carolina guard Phil Ford. The Kings' general manager said yesterday his team wanted Ford, but would take whoever remained available, Ford or Thompson.

Indiana, drafting third, then probably would go for Kentucky center-forward Rick Robey. Indiana's general manager, Bob Leonard, said the Pacers had a list of five players they were considering, depending what happened ahead of them. Those five were Thompson, Ford, Robey, Jackson State foreard Purvis Short and Nevada Las Vegas guard-forward Reggie Theus.

The Knicks also covet Robey, sources said, and may take Bird if the Kentucky star is not available. Golden State, picking fifth, is looking for a strong rebounder, Coach Al Attles said. Boston Coach Tom Sanders said the Celtics are seeking a center and a quick guard.

But sources throughout the league, including Portland's Inman, are convinced that Boston President Red Auerback would pounce on Bird if he still were available as the No. 6 pick overall. Auerback has been his usual silent self on draft matters.

Indiana's coach and general manager, Bob Leonard, was ecstatic over yesterday's developments, which included the Pacers signing 6-8 forward Alex English as a free agent. English was Milwaukee's fifth-leading scorer last season.

Wednesday, sources sais the 76ers and the Pacers had agreed to deal that would send McGinnis and cash to the Pacers so Philadelphia could draft first and take Ford, but that the deal was a 50-50 proposition because McGinnis has a no-trade clause in his contract and his agent was demanding compensation from the 76ers.

"We just couldn't meet the price," 76ers General Manager Pat Williams said yesterday.

Williams said he still was hopeful the 76ers could work out a trade and get into position to draft Ford. "We've laid the groundwork," he said. When you least expect it, something happens."

The order of the draft, barring last minute trades:

1. Portland (from Indiana); 2, Kansas City (from New Jersey); 3, Indiana (from Portland through Buffalo); 4 New York (from New Jersey through Buffalo through Houston); 5, Golden State (from Los Angeles through Kansas City); 6, Boston; 7, Portland from Seattle through Detroit); 8, Boston (from Los Angeles hrough New Orleans); 9, Chicago; 10, Atlanta; 11, New Orleans (from Golden State); 12, Milwaukee (from Cleveland); 13, New Jersey (from New York) 14, Washington; 15, Milwaukee; 16, Atlanta (from new Orleans); 17, Seattle; 18, Washington (from Denver); 19, Phoenix; 20, San Antonio; 21, Philadelphia; 22, Golden State (from Portland).