Former vice president Walter F. Mondale and former Florida governor Reubin Askew yesterday authorized formation of campaign committees for the 1984 Democratic presidential nomination. Two other possible contenders, Rep. Morris K. Udall (D-Ariz.) and Sen. Dale Bumpers (D-Ark.), said they were delaying decisions on entering the race for a few weeks.

The step taken by Mondale and Askew is short of a formal announcement, but assures that money they raise from now on will be eligible for matching from Treasury funds. Sen. Alan Cranston (D-Calif.), another contender, had taken a similar step last Nov. 19.

Udall and Bumpers are interested enough in the race to add their names to the list of speakers at the Jan. 14-16 California Democratic convention in Sacramento that will serve as the kickoff for the presidential chase.

Udall said he was "mighty encouraged" to have finished third in a poll of Democratic voters--behind Mondale and Sen. John H. Glenn (D-Ohio) but ahead of Cranston, Askew and two other senators who will be on stage in Sacramento--Gary Hart of Colorado and Ernest F. Hollings of South Carolina.

The poll of 500 Democrats, taken by the firm of Penn and Schoen after the withdrawal of Sen. Edward M. Kennedy (D-Mass.) last month, gave Mondale 42 percent, Glenn, 18, and Udall, 8, with no one else having more than 3 percent.

But Udall, the runner-up to Jimmy Carter in most of the 1976 primaries, said his family was "unanimously opposed" to his making another race. He conceded that his health presented a barrier, at least in the public mind.

Udall is being treated for Parkinson's disease, and said he has arranged for a panel of three specialists in that illness to examine him and make a full public report. "I feel very strongly I can handle the ordeal" of the campaign, Udall said, "but I don't want to have six press conferences a day where the first question is, 'Tell us about Parkinson's disease.' So we're going to lay it all out openly."

Bumpers said his "visceral decision" was to jump into the race, but said he had decided to delay a decision until he could test his fund-raising potential and the availability of the staffing "that would be necessary for a credible candidacy."

He said he figured he would need to raise "at least $3 million" this year if he were to run.

Udall said he had been encouraged to run by many House colleagues--and by one prominent Republican, Sen. Barry Goldwater of Arizona.

Goldwater wrote: "Mo, you once said nobody from Arizona could be elected president, and I sure went a long way to prove that, but I encourage you to put your hat in the ring. Frankly, I have been favoring John Glenn as the Democratic candidate. I'd much rather see you get in the race since I think you have a real good chance of winning the nomination. Don't turn it down; give it a long, hard thought."

"I'm going to do that," Udall said.