Sen. Richard G. Lugar (R-Ind.) sent formal acceptance to the White House Friday of the president's invitation to lead the U.S. delegation that will observe the Feb. 7 elections in the Philippines.

Critics of the mission have charged that Lugar's presence likely will be interpreted as an endorsement of the election results, particularly because he is chairman of the Senate Foreign Relations Committee. In what Lugar's aides described as a "very carefully worded" letter, Lugar made a point of disclaiming any "seal of approval." He also acknowledged that the delegation's role is not to do what it is incapable of doing, that is, "to certify the validity of the election process."

But officials close to the issue say he has received assurances from the Marcos government that certain "expectations" set out in the letter will be met. "It is my expectation," Lugar wrote, "that observers and the media will have the opportunity to witness the activity in the polling areas, in the tabulation centers and in the Manila headquarters. It is my understanding that NAMFREL (National Citizens Movement for a Free Election) will conduct a 'quick count' " of votes as they are cast -- to establish a number against which the mathematical skills of the government's counters can be tested.

Job Hunting . . . Sources on the Hill say that Rep. Cooper Evans (R-Iowa), who has announced that he will not run for reelection this year, is looking around the Department of Agriculture for future employment. His chances there are considered good, although observers discount him for the No. 2 job as deputy to incoming secretary Richard E. Lyng.

Duane Acker, however, is considered a contender for that spot, largely because his name is being floated by Senate Majority Leader Robert J. Dole. One impediment is that the incumbent deputy, John R. Norton, has given no hint that he wants to resign. But midwesterners are perturbed by a matchup of Lyng, who comes from California, and Norton, whose roots are in Arizona and California, and the betting is that these sensitivities will be acknowledged by USDA. Acker, who is to retire this year as president of Kansas State University, would nicely fit the bill.

Revolving Door . . . It may be nothing more than opportunity knocking, but the latest new policy direction among top-level program managers at the Environmental Protection Agency appears to be out -- preferably into the arms of a law firm with a large environmental practice.

So it is that William N. Hedeman Jr., who headed the "Superfund" program from its inception in 1980 until his transfer to the water division last year, has joined Beveridge & Diamond and its consulting arm, Multinational Business Services Inc. Ruvkin, Radler, Dunne & Bayh gets Courtney Price, who has headed EPA's enforcement and compliance monitoring office since the Great Purge of 1983. John Topping, second in command of the air division, is taking off to form a law partnership with former Federal Election Commission lawyer Donald Swillinger. The new firm will specialize in environmental and election law.

'Dutch' Reagan Returns . . . One American export, at least, is expected to go over well in China, and when a film of Super Bowl XX is broadcast there, some 300 million Chinese will also get to see President Reagan perform an all-new introduction of the game.

A group of Chicago sports fans, magnanimous in the Chicago Bears' 46-10 victory over the New England Patriots, decided to make a film of the game available to Chinese television. And Reagan agreed to return to his sportscaster days and help out with a few words of preamble. A Chinese-language play-by-play will be added next week; Reagan recorded his part Friday.