Like all presidents, Barack Obama is finding it hard to deliver on some of the campaign promises he made last year, in some cases disappointing many ardent supporters who were critical to his election.

Many diverse groups, from gay activists to human rights campaigners to economic reformers, have had their hopes for quick change dashed since Obama took power in January after eight years of Republican President George W. Bush.

The Obama administration this week drew the ire of gay groups for filing a legal brief arguing on behalf of the Defense of Marriage Act, which protects the right of states not to recognize same-sex marriages.

The move prompted prominent gay activist David Mixner to announce on his blog that he would not attend a Democratic Party fundraiser in Washington next week.

How will they ever take us seriously if we keep forking out money while they harm us, Mixner wrote.

Gays are already annoyed Obama has not followed through on a promise to lift the U.S. military's don't ask, don't tell policy barring openly gay people from serving in the military.

Obama, in a step seen as trying to placate the gay community, was announcing on Wednesday the government would extend benefits to same-sex partners of federal employees.

Political experts say Obama is facing what previous presidents have faced -- that fulfilling every campaign promise is impossible -- and they doubt it carries short-term risks.

WELCOME TO GOVERNING

I'd sum it up this way: Welcome to governing, said Larry Sabato, a political science professor at the University of Virginia.

He doubted Obama would be hurt by angering various Democratic constituency groups.

He gets a lot of rope from them. I don't think it will cause him problems for the time being, especially if he delivers on a big topic like healthcare, Sabato said.

Generally, Obama's approach has translated into wide support. An average of recent polls by realclearpolitics.com gave him a strong job approval rating of 60 percent.

Recently, Obama disappointed some on the left by refusing to release photos that are said to depict abuse of terrorism suspects by U.S. interrogators.

He had been poised to release them, but decided against it after being convinced by his military commanders that making them public could trigger a backlash against U.S. troops in Iraq and Afghanistan.

Open-government advocates were troubled that Obama, after promising a policy of transparency, has decided to continue a Bush-era policy of keeping secret White House visitor logs.

Obama found out anew on Wednesday how hard it is to satisfy everyone, announcing a widely anticipated regulatory reform package that left many industry analysts unimpressed.

His decision to add to the Federal Reserve's responsibility in strengthening financial regulation was not a violation of a campaign pledge, but it did disappoint some on the left who wanted a complete overhaul of the regulatory structure.

There are those who will say we did not go far enough, that we should have scrapped the system altogether and started again, Obama said on Wednesday. I think that would be a mistake.

Some liberals are expressing their disappointment with the president, such as comedian Bill Maher, who told CNN he would like to see Obama not care so much if he is popular, not care so much if he is stepping on toes, not care so much if he is expending too much political capital.

I would like to see him lay it on the line and stand up against the energy companies, the banking industry, the healthcare industry, all the corporations who really need to be stood up to, Maher said.

Stephen Hess, a presidential scholar and professor at George Washington University, said promises look entirely different when viewed from the Oval Office, such as his decision not to release the interrogation photos.

There are some pledges that a candidate reverses when he becomes president because things look different. He knows things that he didn't know then, Hess said.

It is also part of the process of compromise that all presidents grapple with when trying to strike a deal with members of the U.S. Congress who have their own ideas on how to tackle a problem, he said.

(Editing by David Storey)

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