Just like Republicans say, if Democrats take control of both the White House and Congress in 2008, taxes will rise, government regulation will increase and domestic spending will grow.

Democrats say so, too. They also promise that their agenda will include more fiscal responsibility, a cleaner environment and greater opportunities for the poor and middle class than Republicans have provided during their rule.

Specifically, Democratic presidential candidates and Congressional leaders are proposing to pass legislation guaranteeing all Americans health insurance, reducing carbon emissions and dependence on foreign oil, increasing federal aid to education from preschool to college, making it easier for unions to organize workers, raising the minimum wage and — to balance the budget — repealing President Bush’s tax cuts for families earning more than $250,000 a year.

In addition, they say they will lift Bush’s limits on stem-cell research, reform the immigration laws, increase the size of the U.S. military, close corporate tax loopholes, eliminate subsidies for oil and gas companies, foster alternative fuel sources and develop new savings programs for the middle class.

How much they actually can get done depends in part on how big Democrats win next November — on whether the incoming president can claim a mandate and whether Democrats have ideological control of the House and a filibuster-proof majority in the Senate.

Democrats currently have a 16-vote margin in the House and are nine votes shy of the 60 necessary to break GOP filibusters without the help of moderate Republicans.

In foreign affairs, margins in Congress count for less, though unified party control guarantees a president running room — even a cheering section. All the Democratic presidential candidates vow that they will withdraw all American combat troops from Iraq. But the two leading contenders, Sens. Hillary Rodham Clinton (N.Y.) and Barack Obama (Ill.), will not promise that all U.S. forces will be gone by the end of their first term.

All the candidates also promise that they will emphasize diplomacy over military power as the means to solve disputes and will use other elements of “soft power” — economic and cultural influence — to rebuild America’s reputation in the world.

One complication is the Democrats’ increasing opposition to free-trade agreements that would open the U.S. market to foreign products — possibly the strongest piece of “soft power” the United States can exert. On the other hand, a Democratic president would have greater persuasive power than a Republican in getting agreements ratified by Congress once he or she negotiated them.

On the domestic side, Sen. Clinton, the frontrunning Democratic presidential candidate, says her highest priority will be enactment of a universal health insurance plan. She says that, after a Democratic Congress rejected her and her husband’s 1993 health care proposal, she is determined not to present a full-blown legislative plan, but merely “principles” for development in consultation with Congress.

The stronger Democratic majorities are, the more likely the final plan is to offer a government-run Medicare-like insurance option to all citizens, which Republicans will castigate as an attempt to enact a Canadian-style single-payer insurance system. Democrats also will surely try to empower Medicare to negotiate prescription drug prices.

A second major priority will be control of global warming and development of alternative energy sources. Clinton proposes to create a $50 billion strategic energy fund, paid for by ending oil and gas subsidies and taxing oil company profits, to develop alternative clean-fuel technology.

Democrats show a distinct partiality toward solar, wind, geothermal and agricultural sources of energy — and increased fuel economy standards for automobiles — as opposed to coal and nuclear power. On the regulatory front, Clinton and other Democratic candidates all are promising stricter environmental controls, such as requirements that utilities generate at least 20 percent of electric power using renewable fuels by 2020. They are likely to be more aggressive in enforcing occupational health and safety laws and oversight of corporate governance, including CEO pay.

On spending, Clinton calculates that her health insurance proposal will cost $110 billion a year — half to be paid for by making the health system more efficient, half by raising taxes on the wealthy. She is proposing to double the budgets of the National Institutes of Health and the National Science Foundation and to establish a government-matched 401(k) savings program for all citizens costing $25 billion per year, paid for by limiting the tax exemption on estates valued at more than $7 million.

She also promises to guarantee all children preschool education at a cost of $10 billion a year, increase federal aid to K-12 education by an unspecified amount and establish an $8 billion a year college-affordability program. She proposes to increase the armed forces by 80,000 personnel and also to end federal “raids” on the Social Security Trust Fund to reduce the government deficit, estimated at $700 billion over the next decade.

This year, the Democratic Congress has re-instituted the “pay-as-you-go” system whereby any new spending is matched by offsets — either tax increases or reduced spending elsewhere. Clinton claims that all of her programs, too, will be “paid for,” although it’s hard to match up all of her offsets.

It’s likely that Democrats would try to pass comprehensive immigration reform and create a bipartisan commission to develop a long-range “fix” for the Social Security system.

The bottom line is that, after eight years of Republican rule in the White House — six of them with Republicans in control of Congress — Democrats are offering “change” as their electoral byword. The election results will determine how much change the country wants.